| Seq | Timestamp | Type | Name | Duration |
|---|---|---|---|---|
| 0/0 | 2026/11/02 00:44 | flow | patch-triage |
3mArgs:null Results: {
"EnableConfigs": [
"BPF_SYSCALL",
"DEBUG_INFO_BTF"
],
"FocusSymbols": [
"bpf_get_call_summary",
"compute_insn_live_regs",
"bpf_compute_live_registers"
],
"KMSANReasoning": "The patch updates BPF verifier liveness analysis (`compute_insn_live_regs`) to account for implicit kfunc arguments. Specifically, it adds an `implicit_slot_cnt` field to `struct bpf_call_summary` so that registers corresponding to kfunc arguments injected implicitly by the verifier are not marked as read/used by the caller program in the live registers bitmask.\n\nKMSAN is not needed because:\n1. `struct bpf_call_summary` is a verifier-internal structure allocated on the stack; its fields (including the new `implicit_slot_cnt`) are explicitly initialized to zero in all branches of `bpf_get_call_summary()` before being read.\n2. The structure is purely internal to the verifier and is never copied to user space (no infoleak risk).\n3. The change affects only the calculation of register bitmasks used for liveness/SCEV analysis during BPF verification. It does not introduce, touch, or expose any uninitialized heap, stack, or page memory, nor does it alter buffer sizing or bounds checking in kernel memory copies.\n4. Any potential issues with verification logic or register state tracking would be caught by verifier assertions and standard tests/KASAN. KMSAN provides no unique detection value here.",
"NeedsKMSAN": false,
"Reasoning": "The patch updates BPF verifier liveness analysis to account for kfuncs with implicit arguments (KF_IMPLICIT_ARGS), ensuring that registers not passed by the BPF program (filled implicitly by the verifier) are not considered used by the call instruction. These changes modify core verifier logic in kernel/bpf/verifier.c and kernel/bpf/liveness.c, reachable from userspace via the bpf(BPF_PROG_LOAD) syscall. Verifier logic regressions can lead to safety check bypasses or verifier crashes, making this patch well worth fuzzing.",
"WorthFuzzing": true
} |
| 1/1 | 2026/11/02 00:44 | action | read-patch-diff |
0mArgs:null Results: {
"PatchDiff": "commit f7f289741506cfdc1b6d997b5a3d95c71da50683\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate: Mon Nov 2 00:44:30 2026 +0000\n\n syz-cluster: applied patch under review\n\ndiff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h\nindex 7baeb831281f38..c28f43d60900c5 100644\n--- a/include/linux/bpf_verifier.h\n+++ b/include/linux/bpf_verifier.h\n@@ -1235,6 +1235,8 @@ static inline bool bpf_ret_reg_pair(struct bpf_verifier_env *env, int subprog)\n \n struct bpf_call_summary {\n \tu8 arg_slot_cnt;\n+\t/* the last of them are filled in by the verifier, the prog doesn't pass them */\n+\tu8 implicit_slot_cnt;\n \tbool is_void;\n \tbool fastcall;\n };\ndiff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c\nindex e657e6d95408f4..215f839bd2fbfe 100644\n--- a/kernel/bpf/liveness.c\n+++ b/kernel/bpf/liveness.c\n@@ -2621,7 +2621,8 @@ static void compute_insn_live_regs(struct bpf_verifier_env *env,\n \t\t\tdef = ALL_CALLER_SAVED_REGS;\n \t\t\tuse = def \u0026 ~BIT(BPF_REG_0);\n \t\t\tif (bpf_get_call_summary(env, insn, \u0026cs)) {\n-\t\t\t\tuse = GENMASK(min_t(u8, cs.arg_slot_cnt, MAX_BPF_FUNC_REG_ARGS), 1);\n+\t\t\t\tuse = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,\n+\t\t\t\t\t\t MAX_BPF_FUNC_REG_ARGS), 1);\n \t\t\t} else if (bpf_pseudo_call(insn)) {\n \t\t\t\t/* a static callee's reads are added in bpf_compute_live_registers() */\n \t\t\t\tsubprog = callee_subprog(env, insn);\ndiff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c\nindex 1b6c0674ff6a13..8509e65889bd15 100644\n--- a/kernel/bpf/verifier.c\n+++ b/kernel/bpf/verifier.c\n@@ -19687,6 +19687,7 @@ bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\n \t\t\t\tbpf_jit_inlines_helper_call(call-\u003eimm));\n \t\tcs-\u003eis_void = fn-\u003eret_type == RET_VOID;\n \t\tcs-\u003earg_slot_cnt = 0;\n+\t\tcs-\u003eimplicit_slot_cnt = 0;\n \t\tfor (i = 0; i \u003c ARRAY_SIZE(fn-\u003earg_type); ++i) {\n \t\t\tif (fn-\u003earg_type[i] == ARG_UNUSED)\n \t\t\t\tbreak;\n@@ -19703,6 +19704,14 @@ bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\n \t\t\t/* error would be reported later */\n \t\t\treturn false;\n \t\tcs-\u003earg_slot_cnt = btf_proto_slots(meta.btf, meta.func_proto);\n+\t\tcs-\u003eimplicit_slot_cnt = 0;\n+\t\tif (meta.kfunc_flags \u0026 KF_IMPLICIT_ARGS) {\n+\t\t\tconst struct btf_type *func = btf_type_by_id(meta.btf, meta.func_id);\n+\n+\t\t\t/* the prototype without implicit args, see is_kfunc_arg_implicit() */\n+\t\t\tcs-\u003eimplicit_slot_cnt = cs-\u003earg_slot_cnt -\n+\t\t\t\tbtf_proto_slots(meta.btf, btf_type_by_id(meta.btf, func-\u003etype));\n+\t\t}\n \t\tcs-\u003efastcall = meta.kfunc_flags \u0026 KF_FASTCALL;\n \t\tcs-\u003eis_void = btf_type_is_void(btf_type_by_id(meta.btf, meta.func_proto-\u003etype));\n \t\treturn true;\ndiff --git a/tools/testing/selftests/bpf/progs/compute_live_registers.c b/tools/testing/selftests/bpf/progs/compute_live_registers.c\nindex 1ff24bbc7beb79..de0496ce7d5e79 100644\n--- a/tools/testing/selftests/bpf/progs/compute_live_registers.c\n+++ b/tools/testing/selftests/bpf/progs/compute_live_registers.c\n@@ -538,6 +538,19 @@ void gotox(void)\n \n #endif /* gotox: x86, arm64, riscv64 */\n \n+extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args,\n+\t\t\t __u32 len__sz) __weak __ksym;\n+\n+/* The verifier fills in the implicit argument of the kfunc. The prog does not pass r5. */\n+SEC(\"syscall\")\n+__log_level(2)\n+__msg(\": .1234..... (85) call bpf_stream_vprintk\")\n+int kfunc_implicit_arg(void *ctx)\n+{\n+\tbpf_stream_printk(1 /* BPF_STDOUT */, \"x\");\n+\treturn 0;\n+}\n+\n /* to retain debug info for BTF generation */\n void kfunc_root(void)\n {\ndiff --git a/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c b/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c\nindex 89b6a47e22dd37..250fc0c7b35578 100644\n--- a/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c\n+++ b/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c\n@@ -27,15 +27,70 @@ int test_kfunc_implicit_arg_impl_illegal(void *ctx)\n }\n \n SEC(\"syscall\")\n+__log_level(2)\n+__msg(\": .12....... (85) call bpf_kfunc_implicit_arg_legacy#\")\n __retval(7)\n int test_kfunc_implicit_arg_legacy(void *ctx)\n {\n \treturn bpf_kfunc_implicit_arg_legacy(3, 4);\n }\n \n+/* The prog passes all three arguments of this kfunc. */\n SEC(\"syscall\")\n+__log_level(2)\n+__msg(\": .123...... (85) call bpf_kfunc_implicit_arg_legacy_impl#\")\n __retval(11)\n int test_kfunc_implicit_arg_legacy_impl(void *ctx)\n {\n \treturn bpf_kfunc_implicit_arg_legacy_impl(5, 6, NULL);\n }\n+\n+/*\n+ * The verifier adds 'r2 = aux' in front of the call. A jump to the call has to\n+ * execute the new insn: the kfunc returns -EINVAL when aux is NULL.\n+ */\n+SEC(\"syscall\")\n+__retval(5)\n+__naked void implicit_arg_jump_to_call(void)\n+{\n+\tasm volatile (\n+\t\"call %[bpf_get_prandom_u32];\"\n+\t\"r1 = 5;\"\n+\t\"r2 = 0;\"\n+\t\"if r0 != 0 goto 1f;\"\n+\t\"r2 = 0;\"\n+\"1:\"\n+\t\"call %[bpf_kfunc_implicit_arg];\"\n+\t\"exit;\"\n+\t:\n+\t: __imm(bpf_get_prandom_u32),\n+\t __imm(bpf_kfunc_implicit_arg)\n+\t: __clobber_all);\n+}\n+\n+/*\n+ * r0 and r1 are live at may_goto, r2 is the first register that is not. The\n+ * insns that the verifier adds for may_goto are free to use r2: 'r2 = aux'\n+ * comes behind them.\n+ */\n+SEC(\"syscall\")\n+__retval(5)\n+__naked void implicit_arg_after_may_goto(void)\n+{\n+\tasm volatile (\n+\t\"r6 = 1;\"\n+\"1:\"\n+\t\"r0 = r6;\"\n+\t\"r1 = r6;\"\n+\t\"may_goto 2f;\"\n+\t\"call %[bpf_kfunc_implicit_arg];\"\n+\t\"if r0 != r6 goto 2f;\"\n+\t\"r6 += 1;\"\n+\t\"if r6 \u003c 5 goto 1b;\"\n+\t\"r0 = r6;\"\n+\"2:\"\n+\t\"exit;\"\n+\t:\n+\t: __imm(bpf_kfunc_implicit_arg)\n+\t: __clobber_all);\n+}\ndiff --git a/tools/testing/selftests/bpf/progs/verifier_scev.c b/tools/testing/selftests/bpf/progs/verifier_scev.c\nindex fa01a616af9d1c..bede3f48fe381c 100644\n--- a/tools/testing/selftests/bpf/progs/verifier_scev.c\n+++ b/tools/testing/selftests/bpf/progs/verifier_scev.c\n@@ -1411,6 +1411,39 @@ __naked void widened_reg_is_not_linked(void)\n \t: __clobber_all);\n }\n \n+extern int bpf_stream_print_stack(int stream_id) __weak __ksym;\n+\n+/*\n+ * The verifier fills in r2, the implicit argument of the kfunc. The call clobbers r2 and nothing\n+ * sets it: if r2 is live at the head of the loop it has no formula.\n+ */\n+SEC(\"syscall\")\n+__success __retval(0)\n+__log_level(2)\n+__msg(\"loop header at 1, header_count is 4 \")\n+__not_msg(\"can't widen\")\n+__naked void kfunc_implicit_arg_in_a_loop(void)\n+{\n+\tasm volatile (\n+\t\"r6 = 0;\"\n+\"1:\"\n+\t\"r1 = 2;\"\n+\t\"call %[bpf_stream_print_stack];\"\n+\t\"r6 += 1;\"\n+\t\"if r6 \u003c 4 goto 1b;\"\n+\t\"r0 = 0;\"\n+\t\"exit;\"\n+\t:\n+\t: __imm(bpf_stream_print_stack)\n+\t: __clobber_all);\n+}\n+\n+/* to retain debug info for BTF generation */\n+void kfunc_root(void)\n+{\n+\tbpf_stream_print_stack(0);\n+}\n+\n /* The unknown SCEV of an unbound STACK_MISC slot must not prevent widening. */\n SEC(\"tracepoint\")\n __success\n"
} |
| 2/1 | 2026/11/02 00:44 | agent | patch-evaluator |
1mModel:core Args: null Results: {
"EnableConfigs": [
"BPF_SYSCALL",
"DEBUG_INFO_BTF"
],
"FocusSymbols": [
"bpf_get_call_summary",
"compute_insn_live_regs",
"bpf_compute_live_registers"
],
"Reasoning": "The patch updates BPF verifier liveness analysis to account for kfuncs with implicit arguments (KF_IMPLICIT_ARGS), ensuring that registers not passed by the BPF program (filled implicitly by the verifier) are not considered used by the call instruction. These changes modify core verifier logic in kernel/bpf/verifier.c and kernel/bpf/liveness.c, reachable from userspace via the bpf(BPF_PROG_LOAD) syscall. Verifier logic regressions can lead to safety check bypasses or verifier crashes, making this patch well worth fuzzing.",
"WorthFuzzing": true
}Instruction: You are an expert Linux kernel maintainer and security engineer.
Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller.
IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on internal assumptions. You must actively use your code access
tools to inspect the actual source code, callers, and surrounding context.
================================================================================
1. CORE TRIAGE PHILOSOPHY
================================================================================
The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs,
and newly triggered assertions introduced by the patch series.
- REACHABILITY IS THE PRIMARY GATE:
Fuzzing can only discover bugs in code that can actually execute in standard virtualized
environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap).
If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed,
regardless of whether it adds assertions or complex logic.
- DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS:
Patch authors routinely label changes as "cleanups", "refactorings", or state
"No functional change intended". Do NOT take these claims at face value.
Code refactorings that rearrange logic, introduce helper functions, or alter state management
in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs.
If reachable executable code is modified or refactored, it MUST be fuzzed.
- NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED:
When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON*, VM_WARN_ON*,
BUG_ON*, lockdep_assert*) in reachable code paths, it enforces new or stricter invariants.
Even if the author believes the invariant always holds, fuzzing is essential to verify whether
an unusual sequence of operations can violate it.
================================================================================
2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA)
================================================================================
Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories:
- Non-kernel and non-executable changes:
* Modifications to Documentation/, comments, or spelling fixes.
* User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/)
that do not affect the compiled kernel image (vmlinux) or kernel modules.
* Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints
that do not alter control flow or data structures.
* Build system or Kconfig changes that do not alter compiled C logic.
- Structurally unreachable hardware:
* Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed,
ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU.
- Unreachable execution paths:
* Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during
physical PCI hot-unplug or manual sysfs driver unbinding.
* Code paths exclusive to architectures other than the target architecture.
================================================================================
3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA)
================================================================================
Return WorthFuzzing=true whenever the patch touches reachable executable code, including:
- Core Subsystems:
* Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/),
BPF, scheduler, core networking, VFS, or syscall handling.
- Refactorings and Code Cleanups:
* Any restructuring of reachable data structures, helper abstractions, or algorithm flows.
- Runtime Assertions and Defensive Checks:
* Any introduction or alteration of assertions (WARN_ON*, VM_WARN_ON*, BUG_ON*, etc.) in reachable paths.
- Reachable Drivers and Protocols:
* Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.).
================================================================================
4. EXTRACTING FocusSymbols (PREVENTING DILUTION)
================================================================================
When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer:
- AVOID UBIQUITOUS LIFECYCLE HOT-PATHS:
Do NOT list generic, ubiquitous functions called by almost every program in the corpus
(including, but not limited to: general memory allocators and deallocators, page fault
and trap handlers, or core synchronization primitives; this is not an exhaustive list).
Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused",
which severely dilutes fuzzing effort away from the actual changes.
- TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS:
List functions that specifically implement the logic being added or altered, or direct API entrypoints
for the subsystem feature under review.
- HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h):
Compiler-inlined static functions (such as static inlines in mm/*.h or include/linux/*.h) lack
distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters.
If the changes are primarily in static inline helpers, identify non-static, feature-specific caller
functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers).
================================================================================
5. IDENTIFYING EnableConfigs
================================================================================
Identify any specific CONFIG_ options required to properly compile and reach the modified code:
- Inspect Kconfig files and #ifdef guards; do not make assumptions.
- Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed.
- Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt: Target architecture: amd64
For your convenience, here is the diff of the changes:
commit f7f289741506cfdc1b6d997b5a3d95c71da50683
Author: syz-cluster <triage@syzkaller.com>
Date: Mon Nov 2 00:44:30 2026 +0000
syz-cluster: applied patch under review
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7baeb831281f38..c28f43d60900c5 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1235,6 +1235,8 @@ static inline bool bpf_ret_reg_pair(struct bpf_verifier_env *env, int subprog)
struct bpf_call_summary {
u8 arg_slot_cnt;
+ /* the last of them are filled in by the verifier, the prog doesn't pass them */
+ u8 implicit_slot_cnt;
bool is_void;
bool fastcall;
};
diff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c
index e657e6d95408f4..215f839bd2fbfe 100644
--- a/kernel/bpf/liveness.c
+++ b/kernel/bpf/liveness.c
@@ -2621,7 +2621,8 @@ static void compute_insn_live_regs(struct bpf_verifier_env *env,
def = ALL_CALLER_SAVED_REGS;
use = def & ~BIT(BPF_REG_0);
if (bpf_get_call_summary(env, insn, &cs)) {
- use = GENMASK(min_t(u8, cs.arg_slot_cnt, MAX_BPF_FUNC_REG_ARGS), 1);
+ use = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,
+ MAX_BPF_FUNC_REG_ARGS), 1);
} else if (bpf_pseudo_call(insn)) {
/* a static callee's reads are added in bpf_compute_live_registers() */
subprog = callee_subprog(env, insn);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1b6c0674ff6a13..8509e65889bd15 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19687,6 +19687,7 @@ bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,
bpf_jit_inlines_helper_call(call->imm));
cs->is_void = fn->ret_type == RET_VOID;
cs->arg_slot_cnt = 0;
+ cs->implicit_slot_cnt = 0;
for (i = 0; i < ARRAY_SIZE(fn->arg_type); ++i) {
if (fn->arg_type[i] == ARG_UNUSED)
break;
@@ -19703,6 +19704,14 @@ bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,
/* error would be reported later */
return false;
cs->arg_slot_cnt = btf_proto_slots(meta.btf, meta.func_proto);
+ cs->implicit_slot_cnt = 0;
+ if (meta.kfunc_flags & KF_IMPLICIT_ARGS) {
+ const struct btf_type *func = btf_type_by_id(meta.btf, meta.func_id);
+
+ /* the prototype without implicit args, see is_kfunc_arg_implicit() */
+ cs->implicit_slot_cnt = cs->arg_slot_cnt -
+ btf_proto_slots(meta.btf, btf_type_by_id(meta.btf, func->type));
+ }
cs->fastcall = meta.kfunc_flags & KF_FASTCALL;
cs->is_void = btf_type_is_void(btf_type_by_id(meta.btf, meta.func_proto->type));
return true;
diff --git a/tools/testing/selftests/bpf/progs/compute_live_registers.c b/tools/testing/selftests/bpf/progs/compute_live_registers.c
index 1ff24bbc7beb79..de0496ce7d5e79 100644
--- a/tools/testing/selftests/bpf/progs/compute_live_registers.c
+++ b/tools/testing/selftests/bpf/progs/compute_live_registers.c
@@ -538,6 +538,19 @@ void gotox(void)
#endif /* gotox: x86, arm64, riscv64 */
+extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args,
+ __u32 len__sz) __weak __ksym;
+
+/* The verifier fills in the implicit argument of the kfunc. The prog does not pass r5. */
+SEC("syscall")
+__log_level(2)
+__msg(": .1234..... (85) call bpf_stream_vprintk")
+int kfunc_implicit_arg(void *ctx)
+{
+ bpf_stream_printk(1 /* BPF_STDOUT */, "x");
+ return 0;
+}
+
/* to retain debug info for BTF generation */
void kfunc_root(void)
{
diff --git a/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c b/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c
index 89b6a47e22dd37..250fc0c7b35578 100644
--- a/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c
+++ b/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c
@@ -27,15 +27,70 @@ int test_kfunc_implicit_arg_impl_illegal(void *ctx)
}
SEC("syscall")
+__log_level(2)
+__msg(": .12....... (85) call bpf_kfunc_implicit_arg_legacy#")
__retval(7)
int test_kfunc_implicit_arg_legacy(void *ctx)
{
return bpf_kfunc_implicit_arg_legacy(3, 4);
}
+/* The prog passes all three arguments of this kfunc. */
SEC("syscall")
+__log_level(2)
+__msg(": .123...... (85) call bpf_kfunc_implicit_arg_legacy_impl#")
__retval(11)
int test_kfunc_implicit_arg_legacy_impl(void *ctx)
{
return bpf_kfunc_implicit_arg_legacy_impl(5, 6, NULL);
}
+
+/*
+ * The verifier adds 'r2 = aux' in front of the call. A jump to the call has to
+ * execute the new insn: the kfunc returns -EINVAL when aux is NULL.
+ */
+SEC("syscall")
+__retval(5)
+__naked void implicit_arg_jump_to_call(void)
+{
+ asm volatile (
+ "call %[bpf_get_prandom_u32];"
+ "r1 = 5;"
+ "r2 = 0;"
+ "if r0 != 0 goto 1f;"
+ "r2 = 0;"
+"1:"
+ "call %[bpf_kfunc_implicit_arg];"
+ "exit;"
+ :
+ : __imm(bpf_get_prandom_u32),
+ __imm(bpf_kfunc_implicit_arg)
+ : __clobber_all);
+}
+
+/*
+ * r0 and r1 are live at may_goto, r2 is the first register that is not. The
+ * insns that the verifier adds for may_goto are free to use r2: 'r2 = aux'
+ * comes behind them.
+ */
+SEC("syscall")
+__retval(5)
+__naked void implicit_arg_after_may_goto(void)
+{
+ asm volatile (
+ "r6 = 1;"
+"1:"
+ "r0 = r6;"
+ "r1 = r6;"
+ "may_goto 2f;"
+ "call %[bpf_kfunc_implicit_arg];"
+ "if r0 != r6 goto 2f;"
+ "r6 += 1;"
+ "if r6 < 5 goto 1b;"
+ "r0 = r6;"
+"2:"
+ "exit;"
+ :
+ : __imm(bpf_kfunc_implicit_arg)
+ : __clobber_all);
+}
diff --git a/tools/testing/selftests/bpf/progs/verifier_scev.c b/tools/testing/selftests/bpf/progs/verifier_scev.c
index fa01a616af9d1c..bede3f48fe381c 100644
--- a/tools/testing/selftests/bpf/progs/verifier_scev.c
+++ b/tools/testing/selftests/bpf/progs/verifier_scev.c
@@ -1411,6 +1411,39 @@ __naked void widened_reg_is_not_linked(void)
: __clobber_all);
}
+extern int bpf_stream_print_stack(int stream_id) __weak __ksym;
+
+/*
+ * The verifier fills in r2, the implicit argument of the kfunc. The call clobbers r2 and nothing
+ * sets it: if r2 is live at the head of the loop it has no formula.
+ */
+SEC("syscall")
+__success __retval(0)
+__log_level(2)
+__msg("loop header at 1, header_count is 4 ")
+__not_msg("can't widen")
+__naked void kfunc_implicit_arg_in_a_loop(void)
+{
+ asm volatile (
+ "r6 = 0;"
+"1:"
+ "r1 = 2;"
+ "call %[bpf_stream_print_stack];"
+ "r6 += 1;"
+ "if r6 < 4 goto 1b;"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_stream_print_stack)
+ : __clobber_all);
+}
+
+/* to retain debug info for BTF generation */
+void kfunc_root(void)
+{
+ bpf_stream_print_stack(0);
+}
+
/* The unknown SCEV of an unbound STACK_MISC slot must not prevent widening. */
SEC("tracepoint")
__success
|
| 3/2 | 2026/11/02 00:44 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 5663 output: 34 thoughts: 554 Thoughts: **My Initial Thoughts on This BPF Patch Series** Okay, so the task at hand is to evaluate a patch series for the Linux kernel. Looking at the affected files, it's clear this is touching the BPF core verifier logic. Specifically, the following files and directories are impacted: `include/linux/bpf_verifier.h`, `kernel/bpf/liveness.c`, `kernel/bpf/verifier.c`, and the BPF selftests directory. It looks like the `bpf_call_summary` struct is getting a new member: `u8 implicit_slot_cnt`. This immediately flags my attention. This indicates a focus on how the verifier handles implicit arguments in BPF function calls, particularly within the context of kfuncs. In `kernel/bpf/liveness.c`, the `compute_insn_live_regs` function has been modified. The key change is in how the argument slot count (`cs.arg_slot_cnt`) is used. Instead of directly using `cs.arg_slot_cnt`, it's now being adjusted by `cs.implicit_slot_cnt` before masking the register usage. This adjustment strongly implies that the code is taking into account the impact of implicit arguments on the register usage. Diving into `kernel/bpf/verifier.c`, I see how this `implicit_slot_cnt` is being populated within `bpf_get_call_summary`. The code now calculates the number of implicit arguments based on whether the `KF_IMPLICIT_ARGS` flag is set in the kfunc metadata. Then it compares the explicit argument count to the total argument count to arrive at the implicit count. This makes sense. So, this patch series is targeting the liveness analysis within the BPF verifier for kfuncs that have implicit arguments. Liveness analysis is absolutely critical for the performance and correctness of BPF programs, influencing register allocation, spilling, dead code elimination, and loop optimization. It's a fundamental aspect of the verifier's ability to optimize the bytecode. Given that BPF is a core subsystem and accessible via the `bpf(BPF_PROG_LOAD, ...)` syscall, even seemingly small changes to the verifier require close scrutiny. It's time to dig into the surrounding code and context with my usual tools to see how this fits in. |
| 4/2 | 2026/11/02 00:44 | tool | grepper |
0mArgs:{
"Expression": "bpf_get_call_summary",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/liveness.c=1742=static int record_call_access(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-1768-\t\targ_slot_cnt = MAX_BPF_FUNC_REG_ARGS + MAX_STACK_ARG_SLOTS;\nkernel/bpf/liveness.c:1769:\telse if (bpf_get_call_summary(env, insn, \u0026cs))\nkernel/bpf/liveness.c-1770-\t\targ_slot_cnt = cs.arg_slot_cnt;\n--\nkernel/bpf/liveness.c=2482=static void compute_insn_live_regs(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-2622-\t\t\tuse = def \u0026 ~BIT(BPF_REG_0);\nkernel/bpf/liveness.c:2623:\t\t\tif (bpf_get_call_summary(env, insn, \u0026cs)) {\nkernel/bpf/liveness.c-2624-\t\t\t\tuse = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,\n--\nkernel/bpf/scev.c=1132=static u16 call_params_mask(struct bpf_verifier_env *env, int idx)\n--\nkernel/bpf/scev.c-1135-\tstruct bpf_call_summary cs;\nkernel/bpf/scev.c:1136:\tint n = bpf_get_call_summary(env, insn, \u0026cs) ? cs.arg_slot_cnt : MAX_BPF_FUNC_REG_ARGS;\nkernel/bpf/scev.c-1137-\n--\nkernel/bpf/verifier.c=19655=bool bpf_verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)\n--\nkernel/bpf/verifier.c-19673- */\nkernel/bpf/verifier.c:19674:bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\nkernel/bpf/verifier.c-19675-\t\t\t struct bpf_call_summary *cs)\n--\nkernel/bpf/verifier.c=19801=static void mark_fastcall_pattern_for_call(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-19812-\nkernel/bpf/verifier.c:19813:\tif (!bpf_get_call_summary(env, call, \u0026cs))\nkernel/bpf/verifier.c-19814-\t\treturn;\n"
} |
| 5/2 | 2026/11/02 00:44 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 7460 output: 38 thoughts: 26 Thoughts: Okay, let's dive into this. Here's my thought process on tackling this particular piece of code: **Inspecting `compute_insn_live_regs` in `kernel/bpf/liveness.c`** Alright, time to get my hands dirty. I need to understand how register liveness is calculated for BPF instructions, and `compute_insn_live_regs` in `kernel/bpf/liveness.c` seems like the place to start. Given my expertise, I'm already anticipating the typical challenges: dealing with control flow graphs, handling different instruction types, and keeping track of register definitions and uses. I'll need to dissect how the function iterates through the instructions, how it tracks register dependencies, and how it handles potential merges at branch points. I'll likely be looking for the core logic that propagates live register information backwards through the code. I'll be focused on efficiency - the algorithm must be performant as this analysis runs frequently, so I'll also be trying to understand and optimize this function to make sure that the BPF programs continue to run at maximum speed. This is important to allow the BPF to provide useful features that are as fast as possible. |
| 6/2 | 2026/11/02 00:44 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/liveness.c",
"FirstLine": 2610,
"LineCount": 40
}Results: {
"Contents": "2610:\t\t\t\t\tuse = 0;\n2611:\t\t\t\tbreak;\n2612:\t\t\tcase BPF_JCOND:\n2613:\t\t\t\tdef = 0;\n2614:\t\t\t\tuse = 0;\n2615:\t\t\t\tbreak;\n2616:\t\t\tcase BPF_EXIT:\n2617:\t\t\t\tdef = 0;\n2618:\t\t\t\tuse = ret_reg_pair ? (r0 | r2) : r0;\n2619:\t\t\t\tbreak;\n2620:\t\t\tcase BPF_CALL:\n2621:\t\t\t\tdef = ALL_CALLER_SAVED_REGS;\n2622:\t\t\t\tuse = def \u0026 ~BIT(BPF_REG_0);\n2623:\t\t\t\tif (bpf_get_call_summary(env, insn, \u0026cs)) {\n2624:\t\t\t\t\tuse = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,\n2625:\t\t\t\t\t\t\t MAX_BPF_FUNC_REG_ARGS), 1);\n2626:\t\t\t\t} else if (bpf_pseudo_call(insn)) {\n2627:\t\t\t\t\t/* a static callee's reads are added in bpf_compute_live_registers() */\n2628:\t\t\t\t\tsubprog = callee_subprog(env, insn);\n2629:\t\t\t\t\tif (bpf_subprog_is_global(env, subprog)) {\n2630:\t\t\t\t\t\treg_args = min_t(u8, env-\u003esubprog_info[subprog].arg_slot_cnt, MAX_BPF_FUNC_REG_ARGS);\n2631:\t\t\t\t\t\tuse = GENMASK(reg_args, 1);\n2632:\t\t\t\t\t} else {\n2633:\t\t\t\t\t\tuse = 0;\n2634:\t\t\t\t\t}\n2635:\t\t\t\t}\n2636:\t\t\t\tdef = mask_widen(def);\n2637:\t\t\t\tuse = mask_widen(use);\n2638:\t\t\t\t/* callx reads the address of the callee from dst_reg */\n2639:\t\t\t\tif (bpf_is_callx(insn))\n2640:\t\t\t\t\tuse |= dst;\n2641:\t\t\t\tbreak;\n2642:\t\t\tdefault:\n2643:\t\t\t\tdef = 0;\n2644:\t\t\t\tuse = class == BPF_JMP ? dst : dst32;\n2645:\t\t\t\tif (BPF_SRC(insn-\u003ecode) == BPF_X)\n2646:\t\t\t\t\tuse |= class == BPF_JMP ? src : src32;\n2647:\t\t\t}\n2648:\t\t\tbreak;\n2649:\t\t}\n"
} |
| 7/2 | 2026/11/02 00:44 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 8468 output: 34 thoughts: 19 Thoughts: Okay, let's dive into this code. **Investigating the Callers of `compute_insn_live_regs`** Alright, so I need to understand how `compute_insn_live_regs` is being used. Where does this function come into play? My first step is to figure out the call sites. I need to trace back from that function and find out which parts of the system are actually *relying* on its output. Understanding the context of its calls will provide the necessary background to start making any informed judgements or modifications about the function. Let's see what the immediate callers of `compute_insn_live_regs` are. From there, I can begin to grasp the larger implications of that function. |
| 8/2 | 2026/11/02 00:44 | tool | grepper |
0mArgs:{
"Expression": "compute_insn_live_regs",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/liveness.c=2476=static int callee_subprog(struct bpf_verifier_env *env, const struct bpf_insn *insn)\n--\nkernel/bpf/liveness.c-2481-/* Compute info-\u003e{use,def} fields for the instruction */\nkernel/bpf/liveness.c:2482:static void compute_insn_live_regs(struct bpf_verifier_env *env,\nkernel/bpf/liveness.c-2483-\t\t\t\t struct bpf_insn *insn,\n--\nkernel/bpf/liveness.c=2662=int bpf_compute_live_registers(struct bpf_verifier_env *env)\n--\nkernel/bpf/liveness.c-2701-\t\tfor (i = start; i \u003c end; ++i)\nkernel/bpf/liveness.c:2702:\t\t\tcompute_insn_live_regs(env, \u0026insns[i], \u0026state[i], ret_reg_pair);\nkernel/bpf/liveness.c-2703-\t}\n"
} |
| 9/2 | 2026/11/02 00:44 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 8965 output: 34 thoughts: 18 Thoughts: Here's a summary of my thought process: **Investigating Call Sites of `bpf_compute_live_registers`** Alright, let's get down to brass tacks. I need to understand the impact of the function `bpf_compute_live_registers` within this BPF context. The immediate question is: where is this thing actually being used? Knowing the call sites is absolutely crucial to understanding its function, its dependencies, and, ultimately, how changes to it might propagate throughout the system. So, first things first: I'm going to track down every instance where `bpf_compute_live_registers` is invoked. A quick search should reveal the pertinent locations in the codebase. From there, I can begin to assess its significance within the broader system. Knowing the contexts of its invocation will give the insight needed to fully understand the role of this function. |
| 10/2 | 2026/11/02 00:44 | tool | grepper |
0mArgs:{
"Expression": "bpf_compute_live_registers",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/liveness.c=2482=static void compute_insn_live_regs(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-2626-\t\t\t} else if (bpf_pseudo_call(insn)) {\nkernel/bpf/liveness.c:2627:\t\t\t\t/* a static callee's reads are added in bpf_compute_live_registers() */\nkernel/bpf/liveness.c-2628-\t\t\t\tsubprog = callee_subprog(env, insn);\n--\nkernel/bpf/liveness.c-2661- */\nkernel/bpf/liveness.c:2662:int bpf_compute_live_registers(struct bpf_verifier_env *env)\nkernel/bpf/liveness.c-2663-{\n--\nkernel/bpf/verifier.c=23875=int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,\n--\nkernel/bpf/verifier.c-24086-\nkernel/bpf/verifier.c:24087:\tret = bpf_compute_live_registers(env);\nkernel/bpf/verifier.c-24088-\tif (ret \u003c 0)\n"
} |
| 11/2 | 2026/11/02 00:44 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 9545 output: 38 thoughts: 92 Thoughts: Okay, here's my take on those thoughts, framed from my expert perspective: **Diving Deep into BPF Verification** Right, so I've zeroed in on something interesting here. `bpf_compute_live_registers`, that crucial piece for understanding register liveness, is being invoked directly within `bpf_check`. That's no surprise, but it's always good to confirm. And, of course, `bpf_check` *is* the absolute heart of BPF verification – the main entry point we hit whenever a BPF program gets loaded via `sys_bpf(BPF_PROG_LOAD, ...)`. So, every time a new BPF program is submitted, we're going through this process. Now, I want to take a closer look at `bpf_get_call_summary`. I know it's in `kernel/bpf/verifier.c`, but I need to refresh my memory on the interactions here. I want to see how the call summaries are constructed and used in conjunction with register liveness. Let's see how `bpf_compute_live_registers` is utilized within `bpf_get_call_summary` and beyond. I'm keen to understand how this function contributes to the complete liveness analysis within the verifier. |
| 12/2 | 2026/11/02 00:44 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/verifier.c",
"FirstLine": 19670,
"LineCount": 50
}Results: {
"Contents": "19670:\t\n19671:\t/* If @call is a kfunc or helper call, fills @cs and returns true,\n19672:\t * otherwise returns false.\n19673:\t */\n19674:\tbool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\n19675:\t\t\t\t struct bpf_call_summary *cs)\n19676:\t{\n19677:\t\tstruct bpf_call_arg_meta meta;\n19678:\t\tconst struct bpf_func_proto *fn;\n19679:\t\tint i;\n19680:\t\n19681:\t\tif (bpf_helper_call(call)) {\n19682:\t\t\tif (bpf_get_helper_proto(env, call-\u003eimm, \u0026fn) \u003c 0)\n19683:\t\t\t\t/* error would be reported later */\n19684:\t\t\t\treturn false;\n19685:\t\t\tcs-\u003efastcall = fn-\u003eallow_fastcall \u0026\u0026\n19686:\t\t\t\t (bpf_verifier_inlines_helper_call(env, call-\u003eimm) ||\n19687:\t\t\t\t\tbpf_jit_inlines_helper_call(call-\u003eimm));\n19688:\t\t\tcs-\u003eis_void = fn-\u003eret_type == RET_VOID;\n19689:\t\t\tcs-\u003earg_slot_cnt = 0;\n19690:\t\t\tcs-\u003eimplicit_slot_cnt = 0;\n19691:\t\t\tfor (i = 0; i \u003c ARRAY_SIZE(fn-\u003earg_type); ++i) {\n19692:\t\t\t\tif (fn-\u003earg_type[i] == ARG_UNUSED)\n19693:\t\t\t\t\tbreak;\n19694:\t\t\t\tcs-\u003earg_slot_cnt++;\n19695:\t\t\t}\n19696:\t\t\treturn true;\n19697:\t\t}\n19698:\t\n19699:\t\tif (bpf_pseudo_kfunc_call(call)) {\n19700:\t\t\tint err;\n19701:\t\n19702:\t\t\terr = bpf_fetch_kfunc_arg_meta(env, call-\u003eimm, call-\u003eoff, \u0026meta);\n19703:\t\t\tif (err \u003c 0)\n19704:\t\t\t\t/* error would be reported later */\n19705:\t\t\t\treturn false;\n19706:\t\t\tcs-\u003earg_slot_cnt = btf_proto_slots(meta.btf, meta.func_proto);\n19707:\t\t\tcs-\u003eimplicit_slot_cnt = 0;\n19708:\t\t\tif (meta.kfunc_flags \u0026 KF_IMPLICIT_ARGS) {\n19709:\t\t\t\tconst struct btf_type *func = btf_type_by_id(meta.btf, meta.func_id);\n19710:\t\n19711:\t\t\t\t/* the prototype without implicit args, see is_kfunc_arg_implicit() */\n19712:\t\t\t\tcs-\u003eimplicit_slot_cnt = cs-\u003earg_slot_cnt -\n19713:\t\t\t\t\tbtf_proto_slots(meta.btf, btf_type_by_id(meta.btf, func-\u003etype));\n19714:\t\t\t}\n19715:\t\t\tcs-\u003efastcall = meta.kfunc_flags \u0026 KF_FASTCALL;\n19716:\t\t\tcs-\u003eis_void = btf_type_is_void(btf_type_by_id(meta.btf, meta.func_proto-\u003etype));\n19717:\t\t\treturn true;\n19718:\t\t}\n19719:\t\n"
} |
| 13/2 | 2026/11/02 00:44 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 10914 output: 30 thoughts: 343 Thoughts: **Analyzing BPF Verifier Liveness Calculation** Okay, let's break this down. It looks like `bpf_get_call_summary()` is calculating `cs->implicit_slot_cnt` for kfuncs that have `KF_IMPLICIT_ARGS`. And then, in `compute_insn_live_regs()`, we're using that value, specifically `cs.arg_slot_cnt - cs.implicit_slot_cnt`, within a `GENMASK` call. This is crucial because it directly impacts how we determine register liveness for these kfuncs with implicit arguments. The logic here is pretty straightforward – if the kfunc has implicit arguments, those registers aren't being explicitly passed by the BPF program. They're either filled in later by the verifier or not passed at all. So, we need to make sure the verifier *doesn't* treat those registers as "used" (read) at the instruction level. This makes sense; it prevents false positives in liveness analysis, which is critical for optimization and correctness. This happens in the `kernel/bpf/verifier.c` and `kernel/bpf/liveness.c` files. So, is this a path that could be worth fuzzing? Absolutely! The BPF verifier is a prime target, constantly hammered by tools like syzkaller. It’s critical, reachable through the `bpf()` syscall and, crucially, directly affects core verifier analysis, specifically liveness analysis, which underpins the BPF security model. Now, let's make sure we have the correct build environment. We need to check the Kconfig requirements, specifically `CONFIG_BPF_SYSCALL` for the BPF syscall itself. Then, I’ll dig into `kernel/bpf/Makefile` and the associated Kconfig to understand the dependencies and ensure the necessary configuration options for `verifier.c` and `liveness.c` are enabled. |
| 14/2 | 2026/11/02 00:45 | tool | grepper |
0mArgs:{
"Expression": "liveness\\.o",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/Makefile=7=CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)\nkernel/bpf/Makefile-8-\nkernel/bpf/Makefile:9:obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o diagnostics.o loops.o scev.o\nkernel/bpf/Makefile-10-obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o\n"
} |
| 15/2 | 2026/11/02 00:45 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 11874 output: 21 thoughts: 109 Thoughts: **Building the BPF Infrastructure** Okay, so I'm looking at the build process for the BPF syscall implementation. We've got `syscall.o`, `verifier.o`, the usual suspects like `inode.o` and `helpers.o`, and then some more specialized modules like `tnum.o`, `cnum.o`, etc. This looks standard. But wait, what about BTF? I need to quickly confirm that BTF support is enabled. Let me just double-check the `DEBUG_INFO_BTF` configuration option. BTF is pretty fundamental these days, especially with kfuncs. Right, confirming that kfuncs *require* BTF. Makes sense. Okay, now I need to dig a little deeper on how the kernel is handling `KF_IMPLICIT_ARGS`. Let's see how it's defined and where it's actually being *used* within the kernel source. I need to understand the implications of it for a specific build configuration. |
| 16/2 | 2026/11/02 00:45 | tool | grepper |
0mArgs:{
"Expression": "KF_IMPLICIT_ARGS"
}Results: {
"Output": "\nFull output is too long, showing 200 out of 282 lines.\nUse more precise expression or PathPrefixes if possible.\n\nNumber of matching lines per file (11 files in total):\nDocumentation/bpf/kfuncs.rst:3\nDocumentation/translations/it_IT/process/changes.rst:1\ninclude/linux/btf.h:1\nkernel/bpf/helpers.c:16\nkernel/bpf/verifier.c:8\nkernel/sched/ext/cid.c:5\nkernel/sched/ext/ext.c:63\nkernel/sched/ext/idle.c:12\nnet/ipv4/bpf_tcp_ops.c:1\ntools/bpf/resolve_btfids/main.c:5\ntools/testing/selftests/bpf/test_kmods/bpf_testmod.c:3\n\nDocumentation/bpf/kfuncs.rst=491=those kfuncs if and when such discussions occur.\nDocumentation/bpf/kfuncs.rst-492-\nDocumentation/bpf/kfuncs.rst:493:2.5.9 KF_IMPLICIT_ARGS flag\nDocumentation/bpf/kfuncs.rst-494-------------------------------------\nDocumentation/bpf/kfuncs.rst-495-\nDocumentation/bpf/kfuncs.rst:496:The KF_IMPLICIT_ARGS flag is used to indicate that the BPF signature\nDocumentation/bpf/kfuncs.rst-497-of the kfunc is different from it's kernel signature, and the values\n--\nDocumentation/bpf/kfuncs.rst=501=Currently only ``struct bpf_prog_aux *`` type is supported.\nDocumentation/bpf/kfuncs.rst-502-\nDocumentation/bpf/kfuncs.rst:503:A kfunc with KF_IMPLICIT_ARGS flag therefore has two types in BTF: one\nDocumentation/bpf/kfuncs.rst-504-function matching the kernel declaration (with _impl suffix in the\n--\nDocumentation/translations/it_IT/process/changes.rst=150=tardi anche per i moduli. Questo richiede pahole v1.22 o successivo.\nDocumentation/translations/it_IT/process/changes.rst-151-\nDocumentation/translations/it_IT/process/changes.rst:152:Dalla versione 7.0, le kfunc annotate con KF_IMPLICIT_ARGS richiedono pahole\nDocumentation/translations/it_IT/process/changes.rst-153-v1.26 o successivo. Senza questa versione, tali kfunc avranno prototipi BTF\n--\ninclude/linux/btf.h-81-#define KF_ARENA_ARG2 (1 \u003c\u003c 15) /* kfunc takes an arena pointer as its second argument */\ninclude/linux/btf.h:82:#define KF_IMPLICIT_ARGS (1 \u003c\u003c 16) /* kfunc has implicit arguments supplied by the verifier */\ninclude/linux/btf.h-83-#define KF_SPINLOCK_SAFE (1 \u003c\u003c 17) /* kfunc is allowed inside bpf_spin_lock-ed region */\n--\nkernel/bpf/helpers.c=5076=BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)\nkernel/bpf/helpers.c-5077-#endif\nkernel/bpf/helpers.c:5078:BTF_ID_FLAGS(func, bpf_obj_new, KF_ACQUIRE | KF_RET_NULL | KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c-5079-BTF_ID_FLAGS(func, bpf_obj_new_impl, KF_ACQUIRE | KF_RET_NULL)\nkernel/bpf/helpers.c:5080:BTF_ID_FLAGS(func, bpf_percpu_obj_new, KF_ACQUIRE | KF_RET_NULL | KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c-5081-BTF_ID_FLAGS(func, bpf_percpu_obj_new_impl, KF_ACQUIRE | KF_RET_NULL)\nkernel/bpf/helpers.c:5082:BTF_ID_FLAGS(func, bpf_obj_drop, KF_RELEASE | KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c-5083-BTF_ID_FLAGS(func, bpf_obj_drop_impl, KF_RELEASE)\nkernel/bpf/helpers.c:5084:BTF_ID_FLAGS(func, bpf_percpu_obj_drop, KF_RELEASE | KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c-5085-BTF_ID_FLAGS(func, bpf_percpu_obj_drop_impl, KF_RELEASE)\nkernel/bpf/helpers.c=5086=BTF_ID_FLAGS(func, bpf_refcount_acquire,\nkernel/bpf/helpers.c:5087:\t KF_ACQUIRE | KF_RET_NULL | KF_RCU | KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c-5088-BTF_ID_FLAGS(func, bpf_refcount_acquire_impl,\nkernel/bpf/helpers.c-5089-\t KF_ACQUIRE | KF_RET_NULL | KF_RCU | KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c:5090:BTF_ID_FLAGS(func, bpf_list_push_front, KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c-5091-BTF_ID_FLAGS(func, bpf_list_push_front_impl, KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c:5092:BTF_ID_FLAGS(func, bpf_list_push_back, KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c-5093-BTF_ID_FLAGS(func, bpf_list_push_back_impl, KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c:5094:BTF_ID_FLAGS(func, bpf_list_add, KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c-5095-BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL | KF_SPINLOCK_SAFE)\n--\nkernel/bpf/helpers.c=5105=BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE | KF_RET_NULL | KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c:5106:BTF_ID_FLAGS(func, bpf_rbtree_add, KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE)\nkernel/bpf/helpers.c-5107-BTF_ID_FLAGS(func, bpf_rbtree_add_impl, KF_SPINLOCK_SAFE)\n--\nkernel/bpf/helpers.c=5187=BTF_ID_FLAGS(func, bpf_wq_init)\nkernel/bpf/helpers.c:5188:BTF_ID_FLAGS(func, bpf_wq_set_callback, KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c-5189-BTF_ID_FLAGS(func, bpf_wq_start)\n--\nkernel/bpf/helpers.c=5237=BTF_ID_FLAGS(func, bpf_cgroup_read_xattr, KF_RCU)\nkernel/bpf/helpers.c-5238-#endif\nkernel/bpf/helpers.c:5239:BTF_ID_FLAGS(func, bpf_stream_vprintk, KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE | KF_PERFMON)\nkernel/bpf/helpers.c:5240:BTF_ID_FLAGS(func, bpf_stream_print_stack, KF_IMPLICIT_ARGS | KF_SPINLOCK_SAFE | KF_PERFMON)\nkernel/bpf/helpers.c:5241:BTF_ID_FLAGS(func, bpf_task_work_schedule_signal, KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c:5242:BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c:5243:BTF_ID_FLAGS(func, bpf_call_rcu, KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c:5244:BTF_ID_FLAGS(func, bpf_call_rcu_tasks_trace, KF_IMPLICIT_ARGS)\nkernel/bpf/helpers.c-5245-BTF_ID_FLAGS(func, bpf_dynptr_from_file)\n--\nkernel/bpf/verifier.c=3006=static int fetch_kfunc_meta(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-3044-\t/*\nkernel/bpf/verifier.c:3045:\t * An actual prototype of a kfunc with KF_IMPLICIT_ARGS flag\nkernel/bpf/verifier.c-3046-\t * can be found through the counterpart _impl kfunc.\nkernel/bpf/verifier.c-3047-\t */\nkernel/bpf/verifier.c:3048:\tif (kfunc_flags \u0026\u0026 (*kfunc_flags \u0026 KF_IMPLICIT_ARGS))\nkernel/bpf/verifier.c-3049-\t\tfunc_proto = find_kfunc_impl_proto(\u0026env-\u003elog, btf, func_name);\n--\nkernel/bpf/verifier.c=13432=static bool is_kfunc_arg_prog_aux(const struct btf *btf, const struct btf_param *arg)\n--\nkernel/bpf/verifier.c-13437-/*\nkernel/bpf/verifier.c:13438: * A kfunc with KF_IMPLICIT_ARGS has two prototypes in BTF:\nkernel/bpf/verifier.c-13439- * - the _impl prototype with full arg list (meta-\u003efunc_proto)\n--\nkernel/bpf/verifier.c=13444=static bool is_kfunc_arg_implicit(const struct bpf_call_arg_meta *meta, u32 arg_idx)\n--\nkernel/bpf/verifier.c-13448-\nkernel/bpf/verifier.c:13449:\tif (!(meta-\u003ekfunc_flags \u0026 KF_IMPLICIT_ARGS))\nkernel/bpf/verifier.c-13450-\t\treturn false;\n--\nkernel/bpf/verifier.c=19674=bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\n--\nkernel/bpf/verifier.c-19707-\t\tcs-\u003eimplicit_slot_cnt = 0;\nkernel/bpf/verifier.c:19708:\t\tif (meta.kfunc_flags \u0026 KF_IMPLICIT_ARGS) {\nkernel/bpf/verifier.c-19709-\t\t\tconst struct btf_type *func = btf_type_by_id(meta.btf, meta.func_id);\n--\nkernel/bpf/verifier.c=22362=static int btf_id_allow_sleepable(u32 btf_id, unsigned long addr, const struct bpf_prog *prog,\n--\nkernel/bpf/verifier.c-22415- * Resolve the prototype describing a trace target's real ABI. A\nkernel/bpf/verifier.c:22416: * KF_IMPLICIT_ARGS kfunc has its injected args stripped from the public\nkernel/bpf/verifier.c-22417- * prototype, so use the _impl prototype; other targets use their own.\n--\nkernel/bpf/verifier.c=22420=btf_attach_func_proto(struct bpf_verifier_log *log, struct btf *btf, u32 func_id)\n--\nkernel/bpf/verifier.c-22441-\t}\nkernel/bpf/verifier.c:22442:\timplicit = btf_kfunc_check_flag(btf, func_id, KF_IMPLICIT_ARGS);\nkernel/bpf/verifier.c-22443-\tmodule_put(mod);\n--\nkernel/bpf/verifier.c-22445-\tif (implicit == -EINVAL) {\nkernel/bpf/verifier.c:22446:\t\tbpf_log(log, \"kfunc %s has inconsistent KF_IMPLICIT_ARGS\\n\", name);\nkernel/bpf/verifier.c-22447-\t\treturn NULL;\n--\nkernel/sched/ext/cid.c=1003=BTF_KFUNCS_START(scx_kfunc_ids_init_cids)\nkernel/sched/ext/cid.c:1004:BTF_ID_FLAGS(func, scx_bpf_cid_override, KF_IMPLICIT_ARGS | KF_SLEEPABLE)\nkernel/sched/ext/cid.c-1005-BTF_KFUNCS_END(scx_kfunc_ids_init_cids)\n--\nkernel/sched/ext/cid.c=1013=BTF_KFUNCS_START(scx_kfunc_ids_cid)\nkernel/sched/ext/cid.c:1014:BTF_ID_FLAGS(func, scx_bpf_cid_to_cpu, KF_IMPLICIT_ARGS)\nkernel/sched/ext/cid.c:1015:BTF_ID_FLAGS(func, scx_bpf_cid_node, KF_IMPLICIT_ARGS)\nkernel/sched/ext/cid.c:1016:BTF_ID_FLAGS(func, scx_bpf_cpu_to_cid, KF_IMPLICIT_ARGS)\nkernel/sched/ext/cid.c:1017:BTF_ID_FLAGS(func, scx_bpf_cid_topo, KF_IMPLICIT_ARGS)\nkernel/sched/ext/cid.c-1018-BTF_KFUNCS_END(scx_kfunc_ids_cid)\n--\nkernel/sched/ext/ext.c=10157=BTF_KFUNCS_START(scx_kfunc_ids_enqueue_dispatch)\nkernel/sched/ext/ext.c:10158:BTF_ID_FLAGS(func, scx_bpf_dsq_insert, KF_IMPLICIT_ARGS | KF_RCU)\nkernel/sched/ext/ext.c:10159:BTF_ID_FLAGS(func, scx_bpf_dsq_insert___v2, KF_IMPLICIT_ARGS | KF_RCU)\nkernel/sched/ext/ext.c:10160:BTF_ID_FLAGS(func, __scx_bpf_dsq_insert_vtime, KF_IMPLICIT_ARGS | KF_RCU)\nkernel/sched/ext/ext.c-10161-BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime, KF_RCU)\n--\nkernel/sched/ext/ext.c=10502=BTF_KFUNCS_START(scx_kfunc_ids_dispatch)\nkernel/sched/ext/ext.c:10503:BTF_ID_FLAGS(func, scx_bpf_dispatch_nr_slots, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:10504:BTF_ID_FLAGS(func, scx_bpf_dispatch_cancel, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:10505:BTF_ID_FLAGS(func, scx_bpf_dsq_move_to_local, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:10506:BTF_ID_FLAGS(func, scx_bpf_dsq_move_to_local___v2, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c-10507-/* scx_bpf_dsq_move*() also in scx_kfunc_ids_unlocked: callable from unlocked contexts */\n--\nkernel/sched/ext/ext.c=10513=BTF_ID_FLAGS(func, scx_bpf_dsq_reenq_task, KF_RCU)\nkernel/sched/ext/ext.c-10514-#ifdef CONFIG_EXT_SUB_SCHED\nkernel/sched/ext/ext.c:10515:BTF_ID_FLAGS(func, scx_bpf_sub_dispatch, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c-10516-#endif\n--\nkernel/sched/ext/ext.c=10553=BTF_KFUNCS_START(scx_kfunc_ids_cpu_release)\nkernel/sched/ext/ext.c:10554:BTF_ID_FLAGS(func, scx_bpf_reenqueue_local, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c-10555-BTF_KFUNCS_END(scx_kfunc_ids_cpu_release)\n--\nkernel/sched/ext/ext.c=10622=BTF_KFUNCS_START(scx_kfunc_ids_unlocked)\nkernel/sched/ext/ext.c:10623:BTF_ID_FLAGS(func, scx_bpf_create_dsq, KF_IMPLICIT_ARGS | KF_SLEEPABLE)\nkernel/sched/ext/ext.c-10624-/* also in scx_kfunc_ids_dispatch: also callable from ops.dispatch() */\n--\nkernel/sched/ext/ext.c=10629=BTF_ID_FLAGS(func, scx_bpf_dsq_reenq_task, KF_RCU)\nkernel/sched/ext/ext.c-10630-/* also in scx_kfunc_ids_select_cpu: also callable from ops.select_cpu()/ops.enqueue() */\nkernel/sched/ext/ext.c:10631:BTF_ID_FLAGS(func, __scx_bpf_select_cpu_and, KF_IMPLICIT_ARGS | KF_RCU)\nkernel/sched/ext/ext.c-10632-BTF_ID_FLAGS(func, scx_bpf_select_cpu_and, KF_RCU)\nkernel/sched/ext/ext.c:10633:BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_IMPLICIT_ARGS | KF_RCU)\nkernel/sched/ext/ext.c-10634-BTF_KFUNCS_END(scx_kfunc_ids_unlocked)\n--\nkernel/sched/ext/ext.c=12071=BTF_KFUNCS_START(scx_kfunc_ids_any)\nkernel/sched/ext/ext.c:12072:BTF_ID_FLAGS(func, scx_bpf_task_set_slice, KF_IMPLICIT_ARGS | KF_RCU);\nkernel/sched/ext/ext.c:12073:BTF_ID_FLAGS(func, scx_bpf_task_set_dsq_vtime, KF_IMPLICIT_ARGS | KF_RCU);\nkernel/sched/ext/ext.c:12074:BTF_ID_FLAGS(func, scx_bpf_task_set_lazy_resched, KF_IMPLICIT_ARGS | KF_RCU);\nkernel/sched/ext/ext.c:12075:BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12076:BTF_ID_FLAGS(func, scx_bpf_kick_cid, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12077:BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12078:BTF_ID_FLAGS(func, scx_bpf_destroy_dsq, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12079:BTF_ID_FLAGS(func, scx_bpf_dsq_peek, KF_IMPLICIT_ARGS | KF_RCU_PROTECTED | KF_RET_NULL)\nkernel/sched/ext/ext.c:12080:BTF_ID_FLAGS(func, scx_bpf_dsq_reenq, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12081:BTF_ID_FLAGS(func, scx_bpf_reenqueue_local___v2, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12082:BTF_ID_FLAGS(func, bpf_iter_scx_dsq_new, KF_IMPLICIT_ARGS | KF_ITER_NEW | KF_RCU_PROTECTED)\nkernel/sched/ext/ext.c-12083-BTF_ID_FLAGS(func, bpf_iter_scx_dsq_next, KF_ITER_NEXT | KF_RET_NULL)\nkernel/sched/ext/ext.c=12084=BTF_ID_FLAGS(func, bpf_iter_scx_dsq_destroy, KF_ITER_DESTROY)\nkernel/sched/ext/ext.c:12085:BTF_ID_FLAGS(func, scx_bpf_exit_bstr, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12086:BTF_ID_FLAGS(func, scx_bpf_error_bstr, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12087:BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12088:BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12089:BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12090:BTF_ID_FLAGS(func, scx_bpf_cpuperf_set, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12091:BTF_ID_FLAGS(func, scx_bpf_cidperf_cap, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12092:BTF_ID_FLAGS(func, scx_bpf_cidperf_cur, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12093:BTF_ID_FLAGS(func, scx_bpf_cidperf_set, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c-12094-BTF_ID_FLAGS(func, scx_bpf_nr_node_ids)\n--\nkernel/sched/ext/ext.c=12097=BTF_ID_FLAGS(func, scx_bpf_nr_online_cids)\nkernel/sched/ext/ext.c:12098:BTF_ID_FLAGS(func, scx_bpf_online_cmask, KF_IMPLICIT_ARGS | KF_ARENA_RET)\nkernel/sched/ext/ext.c-12099-BTF_ID_FLAGS(func, scx_bpf_this_cid)\n--\nkernel/sched/ext/ext.c=12105=BTF_ID_FLAGS(func, scx_bpf_task_cid, KF_RCU)\nkernel/sched/ext/ext.c:12106:BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_IMPLICIT_ARGS | KF_RET_NULL)\nkernel/sched/ext/ext.c:12107:BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)\nkernel/sched/ext/ext.c:12108:BTF_ID_FLAGS(func, scx_bpf_cid_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)\nkernel/sched/ext/ext.c-12109-BTF_ID_FLAGS(func, scx_bpf_tid_to_task, KF_RET_NULL | KF_RCU_PROTECTED)\nkernel/sched/ext/ext.c=12110=BTF_ID_FLAGS(func, scx_bpf_now)\nkernel/sched/ext/ext.c:12111:BTF_ID_FLAGS(func, scx_bpf_events, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c-12112-#ifdef CONFIG_CGROUP_SCHED\nkernel/sched/ext/ext.c:12113:BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_IMPLICIT_ARGS | KF_RCU | KF_ACQUIRE)\nkernel/sched/ext/ext.c-12114-BTF_ID_FLAGS(func, scx_bpf_cgroup_nr_cpus, KF_RCU)\nkernel/sched/ext/ext.c-12115-#endif\nkernel/sched/ext/ext.c:12116:BTF_ID_FLAGS(func, scx_bpf_sub_grant, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12117:BTF_ID_FLAGS(func, scx_bpf_sub_revoke, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12118:BTF_ID_FLAGS(func, scx_bpf_sub_caps, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12119:BTF_ID_FLAGS(func, scx_bpf_sub_kill_bstr, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c-12120-BTF_KFUNCS_END(scx_kfunc_ids_any)\n--\nkernel/sched/ext/ext.c=12146=BTF_KFUNCS_START(scx_kfunc_ids_no_tracing)\nkernel/sched/ext/ext.c:12147:BTF_ID_FLAGS(func, scx_bpf_cpuperf_set, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12148:BTF_ID_FLAGS(func, scx_bpf_cidperf_set, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12149:BTF_ID_FLAGS(func, scx_bpf_sub_grant, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c:12150:BTF_ID_FLAGS(func, scx_bpf_sub_revoke, KF_IMPLICIT_ARGS)\nkernel/sched/ext/ext.c-12151-BTF_KFUNCS_END(scx_kfunc_ids_no_tracing)\n\n"
} |
| 17/2 | 2026/11/02 00:45 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 19231 output: 22 thoughts: 1693 Thoughts: **Analyzing BPF Kfunc Argument Handling for Fuzzing Focus** Okay, so I'm looking at this patch and noticing a critical change in how the BPF verifier handles kfunc arguments, particularly those flagged with `KF_IMPLICIT_ARGS`. The core of the change revolves around several key functions: `bpf_obj_new`, `bpf_stream_vprintk`, `bpf_call_rcu`, etc. These kfuncs use `KF_IMPLICIT_ARGS`. The verifier, via `bpf_get_call_summary()`, now accounts for these implicit arguments when a BPF program calls such a kfunc. The `bpf_get_call_summary()` function, which now has an `implicit_slot_cnt`, is crucial because its output feeds directly into two critical components: `compute_insn_live_regs()` in `liveness.c` and subsequently into `bpf_compute_live_registers()` during the `bpf_check()` process. This is where the liveness analysis happens. So, the verifier is using the new call summary to compute live registers. Looking at the patch itself, I see a new struct member `implicit_slot_cnt` in `struct bpf_call_summary`. `compute_insn_live_regs` has been modified to subtract this from the argument slot count. And the logic within `bpf_get_call_summary()` itself has been updated to calculate this `implicit_slot_cnt` based on the BPF Type Format (BTF) information. Specifically, it seems to be using BTF to determine the number of implicit arguments. Now, as an expert, I know that this impacts core subsystems: memory management, BPF, and core networking. The patch's impact combined with its location makes it "WorthFuzzing=true," obviously. Given that this patch is worth fuzzing, I need to identify good FocusSymbols. The goal is to avoid general hot-path functions, so I must choose functions which implement the specific logic being added or altered. The main functions directly modified or altered are `bpf_get_call_summary` (in `kernel/bpf/verifier.c`) and `compute_insn_live_regs` (in `kernel/bpf/liveness.c`). The second is static, but is called by `bpf_compute_live_registers()`, which is a distinct non-static symbol. Therefore, I will include `bpf_compute_live_registers()` as a focus symbol. The patch has several other calls of `bpf_get_call_summary()`, including `record_call_access`, `call_params_mask`, and `mark_fastcall_pattern_for_call`. |
| 18/2 | 2026/11/02 00:45 | tool | grepper |
0mArgs:{
"Expression": "bpf_get_call_summary"
}Results: {
"Output": "include/linux/bpf_verifier.h=1882=void bpf_verbose_insn(struct bpf_verifier_env *env, struct bpf_insn *insn);\ninclude/linux/bpf_verifier.h:1883:bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\ninclude/linux/bpf_verifier.h-1884-\t\t\t struct bpf_call_summary *cs);\n--\nkernel/bpf/liveness.c=1742=static int record_call_access(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-1768-\t\targ_slot_cnt = MAX_BPF_FUNC_REG_ARGS + MAX_STACK_ARG_SLOTS;\nkernel/bpf/liveness.c:1769:\telse if (bpf_get_call_summary(env, insn, \u0026cs))\nkernel/bpf/liveness.c-1770-\t\targ_slot_cnt = cs.arg_slot_cnt;\n--\nkernel/bpf/liveness.c=2482=static void compute_insn_live_regs(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-2622-\t\t\tuse = def \u0026 ~BIT(BPF_REG_0);\nkernel/bpf/liveness.c:2623:\t\t\tif (bpf_get_call_summary(env, insn, \u0026cs)) {\nkernel/bpf/liveness.c-2624-\t\t\t\tuse = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,\n--\nkernel/bpf/scev.c=1132=static u16 call_params_mask(struct bpf_verifier_env *env, int idx)\n--\nkernel/bpf/scev.c-1135-\tstruct bpf_call_summary cs;\nkernel/bpf/scev.c:1136:\tint n = bpf_get_call_summary(env, insn, \u0026cs) ? cs.arg_slot_cnt : MAX_BPF_FUNC_REG_ARGS;\nkernel/bpf/scev.c-1137-\n--\nkernel/bpf/verifier.c=19655=bool bpf_verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)\n--\nkernel/bpf/verifier.c-19673- */\nkernel/bpf/verifier.c:19674:bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\nkernel/bpf/verifier.c-19675-\t\t\t struct bpf_call_summary *cs)\n--\nkernel/bpf/verifier.c=19801=static void mark_fastcall_pattern_for_call(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-19812-\nkernel/bpf/verifier.c:19813:\tif (!bpf_get_call_summary(env, call, \u0026cs))\nkernel/bpf/verifier.c-19814-\t\treturn;\n"
} |
| 19/2 | 2026/11/02 00:45 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 22371 output: 31 thoughts: 114 Thoughts: **Examining BPF Verification Functions** Okay, so I'm diving into this BPF code again. Right, `bpf_get_call_summary`... that's a key function, and I remember it's exported across the kernel, specifically from the `kernel/bpf` area. Good, good, it's declared in `include/linux/bpf_verifier.h`, and the actual implementation is over in `kernel/bpf/verifier.c`. Now, I also recall seeing `bpf_compute_live_registers` mentioned. That's another important one, especially concerning register liveness analysis, which I've got to understand to make my analysis complete. Ah, yes, it's *also* declared in that same `include/linux/bpf_verifier.h` header, but the actual implementation is in `kernel/bpf/liveness.c`. Right. Let's start with the header file. I need to refresh my memory on the exact declaration of `bpf_compute_live_registers`. Gotta see the function signature, any related structures, and any associated comments. Time to check that declaration. |
| 20/2 | 2026/11/02 00:45 | tool | grepper |
0mArgs:{
"Expression": "bpf_compute_live_registers",
"PathPrefixes": [
"include/"
]
}Results: {
"Output": "include/linux/bpf_verifier.h=1916=bool bpf_stack_slot_alive(struct bpf_verifier_env *env, u32 frameno, u32 spi);\ninclude/linux/bpf_verifier.h:1917:int bpf_compute_live_registers(struct bpf_verifier_env *env);\ninclude/linux/bpf_verifier.h-1918-\n"
} |
| 21/2 | 2026/11/02 00:45 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 22879 output: 23 thoughts: 468 Thoughts: **Analyzing BPF Liveness and Kconfig Dependencies** Okay, let's break this down. First, I need to confirm something about the `kernel/bpf/liveness.c` file. I need to be sure that the `compute_insn_live_regs` function is static. Yep, it is. That means `bpf_compute_live_registers` is the actual exported function in that file that calls `compute_insn_live_regs`. And, of course, `bpf_get_call_summary` in `kernel/bpf/verifier.c` is the other key function. Now, a crucial question is whether `compute_insn_live_regs` should be included in `FocusSymbols`. Considering how syzkaller operates, it relies on symbols from `/proc/kallsyms`. Static functions in the kernel *usually* appear there unless they're inlined. However, since `bpf_compute_live_registers` is definitely non-static, all three - `bpf_get_call_summary`, `compute_insn_live_regs`, and `bpf_compute_live_registers` - should be included. That's good practice. Next, I need to check the Kconfig dependencies. What Kconfig options are required to enable the BPF verifier and kfuncs with implicit arguments? I have to look at `BPF_SYSCALL` and `DEBUG_INFO_BTF`. I'll search the source to see where `KF_IMPLICIT_ARGS` or `bpf_get_call_summary` or `liveness.o` directly depend on configs. I remember the `kernel/bpf/Makefile` includes: `obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o diagnostics.o loops.o scev.o` so `BPF_SYSCALL` compiles `verifier.o` and `liveness.o`. Now, what about BTF? I should check `DEBUG_INFO_BTF` in either `init/Kconfig` or `lib/Kconfig.debug`. |
| 22/2 | 2026/11/02 00:46 | tool | grepper |
0mArgs:{
"Expression": "config DEBUG_INFO_BTF\\b"
}Results: {
"Output": "lib/Kconfig.debug=378=config DEBUG_INFO_SPLIT\n--\nlib/Kconfig.debug-397-\nlib/Kconfig.debug:398:config DEBUG_INFO_BTF\nlib/Kconfig.debug-399-\tbool \"Generate BTF type information\"\n"
} |
| 23/2 | 2026/11/02 00:46 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 23943 output: 34 thoughts: 19 Thoughts: Okay, here's my interpretation of what's going on, formatted as you requested: **Delving into Kconfig.debug** Alright, let's get down to brass tacks. I need to understand something related to the debugging configuration of this project. My focus is likely around line 398 in the `lib/Kconfig.debug` file. This tells me that this particular configuration file is the right place to be looking for specific debug-related options. The line number suggests I should be looking at a fairly specific section within the file, which means it likely isn't a top-level, general overview, but rather a targeted subsection. Let's see what gems we can dig up there. |
| 24/2 | 2026/11/02 00:46 | tool | read-file |
0mArgs:{
"File": "lib/Kconfig.debug",
"FirstLine": 395,
"LineCount": 30
}Results: {
"Contents": " 395:\t\t to know about the .dwo files and include them.\n 396:\t\t Incompatible with older versions of ccache.\n 397:\t\n 398:\tconfig DEBUG_INFO_BTF\n 399:\t\tbool \"Generate BTF type information\"\n 400:\t\tdepends on !DEBUG_INFO_SPLIT \u0026\u0026 !DEBUG_INFO_REDUCED\n 401:\t\tdepends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST\n 402:\t\tdepends on BPF_SYSCALL\n 403:\t\tdepends on PAHOLE_VERSION \u003e= 122\n 404:\t\t# pahole uses elfutils, which does not have support for Hexagon relocations\n 405:\t\tdepends on !HEXAGON\n 406:\t\thelp\n 407:\t\t Generate deduplicated BTF type information from DWARF debug info.\n 408:\t\t Turning this on requires pahole v1.22 or later, which will convert\n 409:\t\t DWARF type info into equivalent deduplicated BTF type info.\n 410:\t\n 411:\tconfig PAHOLE_HAS_BTF_TAG\n 412:\t\tdef_bool PAHOLE_VERSION \u003e= 123\n 413:\t\tdepends on CC_IS_CLANG\n 414:\t\thelp\n 415:\t\t Decide whether pahole emits btf_tag attributes (btf_type_tag and\n 416:\t\t btf_decl_tag) or not. Currently only clang compiler implements\n 417:\t\t these attributes, so make the config depend on CC_IS_CLANG.\n 418:\t\n 419:\tconfig PAHOLE_HAS_LANG_EXCLUDE\n 420:\t\tdef_bool PAHOLE_VERSION \u003e= 124\n 421:\t\thelp\n 422:\t\t Support for the --lang_exclude flag which makes pahole exclude\n 423:\t\t compilation units from the supplied language. Used in Kbuild to\n 424:\t\t omit Rust CUs which are not supported in version 1.24 of pahole,\n"
} |
| 25/2 | 2026/11/02 00:46 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 24686 output: 23 thoughts: 66 Thoughts: Okay, here's my assessment of the situation: **Kernel Function Dependencies and Configuration Checks** Alright, so `kfuncs` rely on BTF (BTF is crucial for describing data structures used in the BPF programs), which I know in turn necessitates the `CONFIG_DEBUG_INFO_BTF` kernel configuration option. This is the starting point, that's clear. Now, I need to verify that BPF itself, the foundational technology, has its own configuration dependencies. Specifically, I need to confirm whether the BPF syscall functionality needs `CONFIG_BPF_SYSCALL` and then whether BPF requires `CONFIG_BPF` is required to be enabled. I'll need to check the `init/Kconfig` file in the kernel source to get the correct dependencies. Let's dig in and see what's what. |
| 26/2 | 2026/11/02 00:46 | tool | grepper |
0mArgs:{
"Expression": "config BPF_SYSCALL\\b"
}Results: {
"Output": "kernel/bpf/Kconfig=29=menu \"BPF subsystem\"\nkernel/bpf/Kconfig-30-\nkernel/bpf/Kconfig:31:config BPF_SYSCALL\nkernel/bpf/Kconfig-32-\tbool \"Enable bpf() system call\"\n"
} |
| 27/2 | 2026/11/02 00:46 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 25037 output: 34 thoughts: 13 Thoughts: Here's my take on those thoughts, tailored for an expert audience: **Kernel BPF Configuration Exploration** Right, let's dive into `kernel/bpf/Kconfig`. I'm starting here because I need to get a clear picture of the available BPF options and how they're exposed through the kernel configuration. I need to understand what's controllable, what's mandatory, and how it all hangs together. I need to know the defaults, dependencies, and any subtle implications of various configurations. Specifically, I'm looking for things that might affect performance, security posture, or feature availability, particularly anything related to recent enhancements or potential areas of concern that have come up in the community. Time to start digging and see what the build system is allowing us to do. |
| 28/2 | 2026/11/02 00:46 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/Kconfig",
"FirstLine": 30,
"LineCount": 30
}Results: {
"Contents": " 30:\t\n 31:\tconfig BPF_SYSCALL\n 32:\t\tbool \"Enable bpf() system call\"\n 33:\t\tselect BPF\n 34:\t\tselect IRQ_WORK\n 35:\t\tselect NEED_TASKS_RCU\n 36:\t\tselect TASKS_TRACE_RCU\n 37:\t\tselect BINARY_PRINTF\n 38:\t\tselect NET_SOCK_MSG if NET\n 39:\t\tselect NET_XGRESS if NET\n 40:\t\tselect PAGE_POOL if NET\n 41:\t\tdefault n\n 42:\t\thelp\n 43:\t\t Enable the bpf() system call that allows to manipulate BPF programs\n 44:\t\t and maps via file descriptors.\n 45:\t\n 46:\tconfig BPF_JIT\n 47:\t\tbool \"Enable BPF Just In Time compiler\"\n 48:\t\tdepends on BPF\n 49:\t\tdepends on HAVE_CBPF_JIT || HAVE_EBPF_JIT\n 50:\t\tselect EXECMEM\n 51:\t\thelp\n 52:\t\t BPF programs are normally handled by a BPF interpreter. This option\n 53:\t\t allows the kernel to generate native code when a program is loaded\n 54:\t\t into the kernel. This will significantly speed-up processing of BPF\n 55:\t\t programs.\n 56:\t\n 57:\t\t Note, an admin should enable this feature changing:\n 58:\t\t /proc/sys/net/core/bpf_jit_enable\n 59:\t\t /proc/sys/net/core/bpf_jit_harden (optional)\n"
} |
| 29/2 | 2026/11/02 00:46 | llm | patch-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 25670 output: 204 thoughts: 574 Thoughts: **My Assessment of the BPF Verifier Configuration and Targeted Functions** Okay, so I'm focusing on a specific area within the BPF verifier. It looks like `BPF_SYSCALL` and `DEBUG_INFO_BTF` are definitely the crucial kernel configs for this. I need to make sure I haven't missed any other potentially relevant ones, though. I've already identified the key functions: `compute_insn_live_regs` in `kernel/bpf/liveness.c`, and `bpf_get_call_summary`, along with `bpf_compute_live_registers` which are also critical. Let me just double check those functions and their location one last time, in `kernel/bpf/verifier.c` and `kernel/bpf/liveness.c` respectively. Ah, I see that `compute_insn_live_regs` *is* static, while the other two are not. Good, confirms what I expected. Now, let's consolidate everything. This patch aims to correct register liveness calculations in `compute_insn_live_regs` and address call summary handling in `bpf_get_call_summary` for kfuncs with `KF_IMPLICIT_ARGS`. Specifically, it concerns calculating `implicit_slot_cnt` and subtracting it correctly during register calculations. This is all related to correctly handling kfuncs where the verifier injects arguments. The instruction itself is marked as WorthFuzzing, with a concise explanation, and the functions I've identified are also confirmed to be in the `FocusSymbols`. I need to make sure that the system is reachable by way of the `bpf(BPF_PROG_LOAD, ...)` syscall on standard architectures such as amd64, which it is. My `FocusSymbols` are still: `bpf_get_call_summary`, `compute_insn_live_regs`, and `bpf_compute_live_registers`, all reachable through the `BPF_SYSCALL` config. Alright, I've reviewed everything thoroughly. There don't seem to be any gaps, and it all makes logical sense. It looks like it's time to call `set-results`. |
| 30/2 | 2026/11/02 00:46 | tool | set-results |
0mArgs:{
"EnableConfigs": [
"BPF_SYSCALL",
"DEBUG_INFO_BTF"
],
"FocusSymbols": [
"bpf_get_call_summary",
"compute_insn_live_regs",
"bpf_compute_live_registers"
],
"Reasoning": "The patch updates BPF verifier liveness analysis to account for kfuncs with implicit arguments (KF_IMPLICIT_ARGS), ensuring that registers not passed by the BPF program (filled implicitly by the verifier) are not considered used by the call instruction. These changes modify core verifier logic in kernel/bpf/verifier.c and kernel/bpf/liveness.c, reachable from userspace via the bpf(BPF_PROG_LOAD) syscall. Verifier logic regressions can lead to safety check bypasses or verifier crashes, making this patch well worth fuzzing.",
"WorthFuzzing": true
}Results: {
"EnableConfigs": [
"BPF_SYSCALL",
"DEBUG_INFO_BTF"
],
"FocusSymbols": [
"bpf_get_call_summary",
"compute_insn_live_regs",
"bpf_compute_live_registers"
],
"Reasoning": "The patch updates BPF verifier liveness analysis to account for kfuncs with implicit arguments (KF_IMPLICIT_ARGS), ensuring that registers not passed by the BPF program (filled implicitly by the verifier) are not considered used by the call instruction. These changes modify core verifier logic in kernel/bpf/verifier.c and kernel/bpf/liveness.c, reachable from userspace via the bpf(BPF_PROG_LOAD) syscall. Verifier logic regressions can lead to safety check bypasses or verifier crashes, making this patch well worth fuzzing.",
"WorthFuzzing": true
} |
| 31/1 | 2026/11/02 00:46 | action | If |
1mArgs:{
"WorthFuzzing": true
}Results: null |
| 32/2 | 2026/11/02 00:46 | agent | kmsan-evaluator |
1mModel:core Args: null Results: {
"KMSANReasoning": "The patch updates BPF verifier liveness analysis (`compute_insn_live_regs`) to account for implicit kfunc arguments. Specifically, it adds an `implicit_slot_cnt` field to `struct bpf_call_summary` so that registers corresponding to kfunc arguments injected implicitly by the verifier are not marked as read/used by the caller program in the live registers bitmask.\n\nKMSAN is not needed because:\n1. `struct bpf_call_summary` is a verifier-internal structure allocated on the stack; its fields (including the new `implicit_slot_cnt`) are explicitly initialized to zero in all branches of `bpf_get_call_summary()` before being read.\n2. The structure is purely internal to the verifier and is never copied to user space (no infoleak risk).\n3. The change affects only the calculation of register bitmasks used for liveness/SCEV analysis during BPF verification. It does not introduce, touch, or expose any uninitialized heap, stack, or page memory, nor does it alter buffer sizing or bounds checking in kernel memory copies.\n4. Any potential issues with verification logic or register state tracking would be caught by verifier assertions and standard tests/KASAN. KMSAN provides no unique detection value here.",
"NeedsKMSAN": false
}Instruction: You are an expert Linux kernel security engineer specializing in kernel memory
error detectors (KASAN and KMSAN). Your job is to review the provided patch series and
determine if the code changes justify spawning a dedicated KMSAN (KernelMemorySanitizer)
fuzzing session in addition to standard KASAN fuzzing.
CRITICAL DISTINCTION BETWEEN KASAN AND KMSAN:
- Standard KASAN kernel builds (upstream-apparmor-kasan.config) already enable
a comprehensive suite of debugging tools and sanitizers, including KASAN
(out-of-bounds accesses, use-after-free, double free, invalid free), LOCKDEP
(locking bugs and deadlocks), UB-sanitizers, and memory corruption checks.
- KMSAN (KernelMemorySanitizer) detects reads of UNINITIALIZED memory (stack, heap,
or page allocations) and kernel-to-user memory info-leaks.
Rule: THERE IS NO SENSE IN RUNNING A KMSAN SESSION IF A BUG CAN BE CAUGHT BY KASAN,
LOCKDEP, OR OTHER STANDARD BUG DETECTORS.
A dedicated KMSAN fuzzing session incurs significant resource costs. You must ONLY
set NeedsKMSAN=true if the code changes introduce or expose UNINITIALIZED MEMORY risks
that are detected ONLY by KMSAN.
Look holistically at the patch series and surrounding code. Even if no direct
uninitialized field accesses or new buffer allocations are added in the diff itself,
a patch may alter control flow, bounds checking, or data length calculations in ways
that change how the rest of the code operates on existing buffers (e.g. allowing
uninitialized stack/heap memory to be read, copied to user space, or used in control
flow). Do not hesitate to use your code access tools to inspect the surrounding code,
called functions, and callers.
Set NeedsKMSAN=true ONLY IF the patch introduces or modifies:
1. Kernel structures sent to user space (via copy_to_user, put_user, netlink skb
attributes, ioctl output arguments, socket options, or BPF buffers) where fields
or structure padding might not be fully initialized/zeroed.
2. Conditional logic or branching that depends on potentially uninitialized variables
or struct fields.
3. Allocation or initialization of complex data structures where uninitialized fields
could be read later in reachable code paths.
4. Bounds checks, lengths, or logic in a way that allows surrounding code to access
uninitialized bytes of existing buffers.
Set NeedsKMSAN=false IF:
- The code changes primarily risk out-of-bounds access, array overflows, NULL pointer
dereferences, locking deadlocks, or use-after-free bugs (these are already caught
by KASAN, LOCKDEP, or standard bug detectors).
- All stack/heap structures touched or introduced by the patch are fully zeroed
or initialized (e.g. using = {0}, memset, kzalloc) before being read or copied.
- The patch does not introduce any risk of uninitialized memory usage or info-leaks.
Use your code access tools to inspect the surrounding code if necessary, then provide
detailed KMSANReasoning contrasting KASAN vs KMSAN applicability for this patch.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt: Target architecture: amd64
For your convenience, here is the diff of the changes:
commit f7f289741506cfdc1b6d997b5a3d95c71da50683
Author: syz-cluster <triage@syzkaller.com>
Date: Mon Nov 2 00:44:30 2026 +0000
syz-cluster: applied patch under review
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7baeb831281f38..c28f43d60900c5 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1235,6 +1235,8 @@ static inline bool bpf_ret_reg_pair(struct bpf_verifier_env *env, int subprog)
struct bpf_call_summary {
u8 arg_slot_cnt;
+ /* the last of them are filled in by the verifier, the prog doesn't pass them */
+ u8 implicit_slot_cnt;
bool is_void;
bool fastcall;
};
diff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c
index e657e6d95408f4..215f839bd2fbfe 100644
--- a/kernel/bpf/liveness.c
+++ b/kernel/bpf/liveness.c
@@ -2621,7 +2621,8 @@ static void compute_insn_live_regs(struct bpf_verifier_env *env,
def = ALL_CALLER_SAVED_REGS;
use = def & ~BIT(BPF_REG_0);
if (bpf_get_call_summary(env, insn, &cs)) {
- use = GENMASK(min_t(u8, cs.arg_slot_cnt, MAX_BPF_FUNC_REG_ARGS), 1);
+ use = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,
+ MAX_BPF_FUNC_REG_ARGS), 1);
} else if (bpf_pseudo_call(insn)) {
/* a static callee's reads are added in bpf_compute_live_registers() */
subprog = callee_subprog(env, insn);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1b6c0674ff6a13..8509e65889bd15 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19687,6 +19687,7 @@ bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,
bpf_jit_inlines_helper_call(call->imm));
cs->is_void = fn->ret_type == RET_VOID;
cs->arg_slot_cnt = 0;
+ cs->implicit_slot_cnt = 0;
for (i = 0; i < ARRAY_SIZE(fn->arg_type); ++i) {
if (fn->arg_type[i] == ARG_UNUSED)
break;
@@ -19703,6 +19704,14 @@ bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,
/* error would be reported later */
return false;
cs->arg_slot_cnt = btf_proto_slots(meta.btf, meta.func_proto);
+ cs->implicit_slot_cnt = 0;
+ if (meta.kfunc_flags & KF_IMPLICIT_ARGS) {
+ const struct btf_type *func = btf_type_by_id(meta.btf, meta.func_id);
+
+ /* the prototype without implicit args, see is_kfunc_arg_implicit() */
+ cs->implicit_slot_cnt = cs->arg_slot_cnt -
+ btf_proto_slots(meta.btf, btf_type_by_id(meta.btf, func->type));
+ }
cs->fastcall = meta.kfunc_flags & KF_FASTCALL;
cs->is_void = btf_type_is_void(btf_type_by_id(meta.btf, meta.func_proto->type));
return true;
diff --git a/tools/testing/selftests/bpf/progs/compute_live_registers.c b/tools/testing/selftests/bpf/progs/compute_live_registers.c
index 1ff24bbc7beb79..de0496ce7d5e79 100644
--- a/tools/testing/selftests/bpf/progs/compute_live_registers.c
+++ b/tools/testing/selftests/bpf/progs/compute_live_registers.c
@@ -538,6 +538,19 @@ void gotox(void)
#endif /* gotox: x86, arm64, riscv64 */
+extern int bpf_stream_vprintk(int stream_id, const char *fmt__str, const void *args,
+ __u32 len__sz) __weak __ksym;
+
+/* The verifier fills in the implicit argument of the kfunc. The prog does not pass r5. */
+SEC("syscall")
+__log_level(2)
+__msg(": .1234..... (85) call bpf_stream_vprintk")
+int kfunc_implicit_arg(void *ctx)
+{
+ bpf_stream_printk(1 /* BPF_STDOUT */, "x");
+ return 0;
+}
+
/* to retain debug info for BTF generation */
void kfunc_root(void)
{
diff --git a/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c b/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c
index 89b6a47e22dd37..250fc0c7b35578 100644
--- a/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c
+++ b/tools/testing/selftests/bpf/progs/kfunc_implicit_args.c
@@ -27,15 +27,70 @@ int test_kfunc_implicit_arg_impl_illegal(void *ctx)
}
SEC("syscall")
+__log_level(2)
+__msg(": .12....... (85) call bpf_kfunc_implicit_arg_legacy#")
__retval(7)
int test_kfunc_implicit_arg_legacy(void *ctx)
{
return bpf_kfunc_implicit_arg_legacy(3, 4);
}
+/* The prog passes all three arguments of this kfunc. */
SEC("syscall")
+__log_level(2)
+__msg(": .123...... (85) call bpf_kfunc_implicit_arg_legacy_impl#")
__retval(11)
int test_kfunc_implicit_arg_legacy_impl(void *ctx)
{
return bpf_kfunc_implicit_arg_legacy_impl(5, 6, NULL);
}
+
+/*
+ * The verifier adds 'r2 = aux' in front of the call. A jump to the call has to
+ * execute the new insn: the kfunc returns -EINVAL when aux is NULL.
+ */
+SEC("syscall")
+__retval(5)
+__naked void implicit_arg_jump_to_call(void)
+{
+ asm volatile (
+ "call %[bpf_get_prandom_u32];"
+ "r1 = 5;"
+ "r2 = 0;"
+ "if r0 != 0 goto 1f;"
+ "r2 = 0;"
+"1:"
+ "call %[bpf_kfunc_implicit_arg];"
+ "exit;"
+ :
+ : __imm(bpf_get_prandom_u32),
+ __imm(bpf_kfunc_implicit_arg)
+ : __clobber_all);
+}
+
+/*
+ * r0 and r1 are live at may_goto, r2 is the first register that is not. The
+ * insns that the verifier adds for may_goto are free to use r2: 'r2 = aux'
+ * comes behind them.
+ */
+SEC("syscall")
+__retval(5)
+__naked void implicit_arg_after_may_goto(void)
+{
+ asm volatile (
+ "r6 = 1;"
+"1:"
+ "r0 = r6;"
+ "r1 = r6;"
+ "may_goto 2f;"
+ "call %[bpf_kfunc_implicit_arg];"
+ "if r0 != r6 goto 2f;"
+ "r6 += 1;"
+ "if r6 < 5 goto 1b;"
+ "r0 = r6;"
+"2:"
+ "exit;"
+ :
+ : __imm(bpf_kfunc_implicit_arg)
+ : __clobber_all);
+}
diff --git a/tools/testing/selftests/bpf/progs/verifier_scev.c b/tools/testing/selftests/bpf/progs/verifier_scev.c
index fa01a616af9d1c..bede3f48fe381c 100644
--- a/tools/testing/selftests/bpf/progs/verifier_scev.c
+++ b/tools/testing/selftests/bpf/progs/verifier_scev.c
@@ -1411,6 +1411,39 @@ __naked void widened_reg_is_not_linked(void)
: __clobber_all);
}
+extern int bpf_stream_print_stack(int stream_id) __weak __ksym;
+
+/*
+ * The verifier fills in r2, the implicit argument of the kfunc. The call clobbers r2 and nothing
+ * sets it: if r2 is live at the head of the loop it has no formula.
+ */
+SEC("syscall")
+__success __retval(0)
+__log_level(2)
+__msg("loop header at 1, header_count is 4 ")
+__not_msg("can't widen")
+__naked void kfunc_implicit_arg_in_a_loop(void)
+{
+ asm volatile (
+ "r6 = 0;"
+"1:"
+ "r1 = 2;"
+ "call %[bpf_stream_print_stack];"
+ "r6 += 1;"
+ "if r6 < 4 goto 1b;"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_stream_print_stack)
+ : __clobber_all);
+}
+
+/* to retain debug info for BTF generation */
+void kfunc_root(void)
+{
+ bpf_stream_print_stack(0);
+}
+
/* The unknown SCEV of an unbound STACK_MISC slot must not prevent widening. */
SEC("tracepoint")
__success
|
| 33/3 | 2026/11/02 00:46 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 4875 output: 34 thoughts: 1192 Thoughts: **KMSAN Fuzzing Session Justification: BPF Verifier Patch** Okay, let's break this down. The objective is to determine if this patch series warrants a KMSAN fuzzing session. The guiding principle is clear: avoid KMSAN if standard bug detectors (KASAN, LOCKDEP, etc.) can catch the issues. So, the question is: does this patch introduce novel areas where uninitialized memory access might be exposed, or is it dealing with bugs that are already in the purview of other detectors? First, I need to internalize these rules: the critical flags for NeedsKMSAN are triggered if there are changes touching userspace with possible padding issues, conditional logic dependent on uninitialized variables, allocation of complex structs where uninitialized fields are read, or the patch allows for accesses to uninitialized bytes of buffers. And a flag is *not* necessary if standard problems are present (out-of-bounds, use-after-free, etc.), if new/modified structs are fully initialized, or if there's no risk of information leaks due to uninitialized memory. Looking at the patch itself, it modifies `include/linux/bpf_verifier.h`, `kernel/bpf/liveness.c`, `kernel/bpf/verifier.c` and Selftests under `tools/testing/selftests/bpf/progs/...`. The core of the changes revolve around an updated `struct bpf_call_summary` and its usage within the BPF verifier. Specifically, the addition of `implicit_slot_cnt` and modifications to how argument slot counts are handled during BPF program analysis. The changes seem to affect the BPF verifier's ability to accurately determine which registers are live during a BPF function call. The relevant code changes are in the `bpf_get_call_summary` function where the `implicit_slot_cnt` field is now populated, and that value is used in the `liveness.c` file. This is crucial: the verifier is a tricky part of the kernel, and subtle changes can have unintended side-effects. So, let's dig deeper, I need to know the context: where is `bpf_get_call_summary` used? And what happens when a call summary is updated in `compute_insn_live_regs`? The next step is a deep dive into the source, specifically looking at `kernel/bpf/liveness.c` and `kernel/bpf/verifier.c`. Tools like `grepper` (or just reading the files directly) will be essential for mapping this out. I'll need to understand how the new `implicit_slot_cnt` influences register liveness calculations and, more importantly, if this introduces any opportunity for uninitialized memory to leak or become exposed in a way that *isn't* caught by existing checks. My concern is whether this new counter makes the verifier's behavior dependent on potentially uninitialized fields in the `bpf_call_summary` structure or in related structures. I need to be sure that the computation of the `use` variable (in `liveness.c`) does not lead to potential leaks or corruption. The selftests are a good sign; if they include a test for this change, that would suggest that existing test coverage can cover this area. But even if there are selftests, I still need to satisfy myself that the change is safe. Ultimately, whether KMSAN is needed boils down to whether the changes introduce a *new* avenue for uninitialized memory usage/information leaks. If this patch introduces logic that conditionally reads or uses newly introduced fields, especially those related to slot counts, without complete initialization, then KMSAN is warranted. If not, if the changes primarily affect existing analysis or optimization, or if new fields are guaranteed to be initialized, then existing detectors should suffice. |
| 34/3 | 2026/11/02 00:46 | tool | grepper |
0mArgs:{
"Expression": "bpf_get_call_summary",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/liveness.c=1742=static int record_call_access(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-1768-\t\targ_slot_cnt = MAX_BPF_FUNC_REG_ARGS + MAX_STACK_ARG_SLOTS;\nkernel/bpf/liveness.c:1769:\telse if (bpf_get_call_summary(env, insn, \u0026cs))\nkernel/bpf/liveness.c-1770-\t\targ_slot_cnt = cs.arg_slot_cnt;\n--\nkernel/bpf/liveness.c=2482=static void compute_insn_live_regs(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-2622-\t\t\tuse = def \u0026 ~BIT(BPF_REG_0);\nkernel/bpf/liveness.c:2623:\t\t\tif (bpf_get_call_summary(env, insn, \u0026cs)) {\nkernel/bpf/liveness.c-2624-\t\t\t\tuse = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,\n--\nkernel/bpf/scev.c=1132=static u16 call_params_mask(struct bpf_verifier_env *env, int idx)\n--\nkernel/bpf/scev.c-1135-\tstruct bpf_call_summary cs;\nkernel/bpf/scev.c:1136:\tint n = bpf_get_call_summary(env, insn, \u0026cs) ? cs.arg_slot_cnt : MAX_BPF_FUNC_REG_ARGS;\nkernel/bpf/scev.c-1137-\n--\nkernel/bpf/verifier.c=19655=bool bpf_verifier_inlines_helper_call(struct bpf_verifier_env *env, s32 imm)\n--\nkernel/bpf/verifier.c-19673- */\nkernel/bpf/verifier.c:19674:bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\nkernel/bpf/verifier.c-19675-\t\t\t struct bpf_call_summary *cs)\n--\nkernel/bpf/verifier.c=19801=static void mark_fastcall_pattern_for_call(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-19812-\nkernel/bpf/verifier.c:19813:\tif (!bpf_get_call_summary(env, call, \u0026cs))\nkernel/bpf/verifier.c-19814-\t\treturn;\n"
} |
| 35/3 | 2026/11/02 00:46 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 7624 output: 38 thoughts: 87 Thoughts: Here's my analysis of the provided code inspection request, from my perspective as a seasoned BPF expert: **Diving into BPF Liveness Analysis in the Kernel** Okay, I see the task. We're getting into the nitty-gritty of BPF liveness analysis. The goal is likely to understand how register liveness is tracked, specifically within the BPF interpreter. My initial thought is to zero in on two key functions: `record_call_access` and `compute_insn_live_regs`. `record_call_access` is probably responsible for tracking register usage across function calls, which is crucial for determining which registers remain 'live' after a call. `compute_insn_live_regs`, on the other hand, likely calculates the live registers at a *single* instruction level, feeding into the larger analysis. We also need to consider `bpf_get_call_summary`. The specified line ranges – around 1740-1780 and 2610-2640 in `kernel/bpf/liveness.c` – give us a good starting point. I'm guessing the first range houses code related to `record_call_access` and the mechanics of capturing register usage within a BPF call. The second range, likely delves into the intricacies of `compute_insn_live_regs`, perhaps showing the algorithm used to determine register liveness given the instruction type and preceding state. My gut tells me these line numbers bracket the core logic for the analysis. I'll read with that in mind and be sure to look for any data structures, like bitsets, that are used to track register liveness. Let's see what gems are there. |
| 36/3 | 2026/11/02 00:46 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/liveness.c",
"FirstLine": 1760,
"LineCount": 30
}Results: {
"Contents": "1760:\t\t\targ_slot_cnt = MAX_BPF_FUNC_ARGS;\n1761:\t\t} else if (bpf_is_callx(insn))\n1762:\t\t\t/*\n1763:\t\t\t * The callee is not known statically. Assume that all arg\n1764:\t\t\t * slots are passed and let record_arg_access() conservatively\n1765:\t\t\t * mark the stack of all frames as read if any of them is\n1766:\t\t\t * derived from a frame pointer.\n1767:\t\t\t */\n1768:\t\t\targ_slot_cnt = MAX_BPF_FUNC_REG_ARGS + MAX_STACK_ARG_SLOTS;\n1769:\t\telse if (bpf_get_call_summary(env, insn, \u0026cs))\n1770:\t\t\targ_slot_cnt = cs.arg_slot_cnt;\n1771:\t\n1772:\t\tfor (r = BPF_REG_1; r \u003c BPF_REG_1 + min(arg_slot_cnt, MAX_BPF_FUNC_REG_ARGS); r++) {\n1773:\t\t\terr = record_arg_access(env, instance, insn, \u0026at[r], r - 1, insn_idx);\n1774:\t\t\tif (err)\n1775:\t\t\t\treturn err;\n1776:\t\t}\n1777:\t\n1778:\t\tfor (r = 0; r \u003c MAX_STACK_ARG_SLOTS \u0026\u0026 r \u003c arg_slot_cnt - MAX_BPF_FUNC_REG_ARGS; r++) {\n1779:\t\t\terr = record_arg_access(env, instance, insn, \u0026at[MAX_BPF_REG + r],\n1780:\t\t\t\t\t\tr + MAX_BPF_FUNC_REG_ARGS, insn_idx);\n1781:\t\t\tif (err)\n1782:\t\t\t\treturn err;\n1783:\t\t}\n1784:\t\treturn 0;\n1785:\t}\n1786:\t\n1787:\t/*\n1788:\t * For a calls_callback helper, find the callback subprog and determine\n1789:\t * which caller register maps to which callback register for FP passthrough.\n"
} |
| 37/3 | 2026/11/02 00:46 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 8690 output: 38 thoughts: 40 Thoughts: Okay, let's dive into this. **Examining `compute_insn_live_regs` in `kernel/bpf/liveness.c`** Alright, I'm thinking we need to check out the `compute_insn_live_regs` function in the `liveness.c` file within the kernel's BPF section. Specifically, the lines between 2610 and 2640 seem like a good starting point. I want to understand how the liveness analysis is being done at the instruction level within this BPF context. This function likely calculates which registers are considered "live" (meaning their values might be used later) after the execution of a given instruction. I'll need to see how it's determining the impact of each instruction on register liveness, tracing the data flow. This is where the core of the liveness information for BPF programs is likely determined, therefore it's key to the overall optimization strategy. I expect to see the meat of the analysis here. |
| 38/3 | 2026/11/02 00:46 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/liveness.c",
"FirstLine": 2610,
"LineCount": 40
}Results: {
"Contents": "2610:\t\t\t\t\tuse = 0;\n2611:\t\t\t\tbreak;\n2612:\t\t\tcase BPF_JCOND:\n2613:\t\t\t\tdef = 0;\n2614:\t\t\t\tuse = 0;\n2615:\t\t\t\tbreak;\n2616:\t\t\tcase BPF_EXIT:\n2617:\t\t\t\tdef = 0;\n2618:\t\t\t\tuse = ret_reg_pair ? (r0 | r2) : r0;\n2619:\t\t\t\tbreak;\n2620:\t\t\tcase BPF_CALL:\n2621:\t\t\t\tdef = ALL_CALLER_SAVED_REGS;\n2622:\t\t\t\tuse = def \u0026 ~BIT(BPF_REG_0);\n2623:\t\t\t\tif (bpf_get_call_summary(env, insn, \u0026cs)) {\n2624:\t\t\t\t\tuse = GENMASK(min_t(u8, cs.arg_slot_cnt - cs.implicit_slot_cnt,\n2625:\t\t\t\t\t\t\t MAX_BPF_FUNC_REG_ARGS), 1);\n2626:\t\t\t\t} else if (bpf_pseudo_call(insn)) {\n2627:\t\t\t\t\t/* a static callee's reads are added in bpf_compute_live_registers() */\n2628:\t\t\t\t\tsubprog = callee_subprog(env, insn);\n2629:\t\t\t\t\tif (bpf_subprog_is_global(env, subprog)) {\n2630:\t\t\t\t\t\treg_args = min_t(u8, env-\u003esubprog_info[subprog].arg_slot_cnt, MAX_BPF_FUNC_REG_ARGS);\n2631:\t\t\t\t\t\tuse = GENMASK(reg_args, 1);\n2632:\t\t\t\t\t} else {\n2633:\t\t\t\t\t\tuse = 0;\n2634:\t\t\t\t\t}\n2635:\t\t\t\t}\n2636:\t\t\t\tdef = mask_widen(def);\n2637:\t\t\t\tuse = mask_widen(use);\n2638:\t\t\t\t/* callx reads the address of the callee from dst_reg */\n2639:\t\t\t\tif (bpf_is_callx(insn))\n2640:\t\t\t\t\tuse |= dst;\n2641:\t\t\t\tbreak;\n2642:\t\t\tdefault:\n2643:\t\t\t\tdef = 0;\n2644:\t\t\t\tuse = class == BPF_JMP ? dst : dst32;\n2645:\t\t\t\tif (BPF_SRC(insn-\u003ecode) == BPF_X)\n2646:\t\t\t\t\tuse |= class == BPF_JMP ? src : src32;\n2647:\t\t\t}\n2648:\t\t\tbreak;\n2649:\t\t}\n"
} |
| 39/3 | 2026/11/02 00:46 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 9674 output: 38 thoughts: 36 Thoughts: Okay, let's dive into this. Here's my take on those thoughts: **Analyzing `bpf_get_call_summary` in the BPF Verifier** Alright, I'm thinking we need to shift our focus to `bpf_get_call_summary`. I recall it's located in `kernel/bpf/verifier.c`, specifically around line 19680. It's obviously a crucial piece of the puzzle, and I need to re-examine what's happening there in context. It probably relates to the function call analysis portion of the verifier, so it should be interesting to see how the kernel handles and summarizes the specifics. I'm imagining it'll be related to tracking function calls within the BPF program for safety and optimization. I'll need to drill down and understand how it interacts with the broader verification process and what kind of information it's extracting. I'm expecting this will provide insight into how the verifier ultimately makes its decisions about whether a BPF program is safe to load. Let's see what gems are there! |
| 40/3 | 2026/11/02 00:47 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/verifier.c",
"FirstLine": 19670,
"LineCount": 55
}Results: {
"Contents": "19670:\t\n19671:\t/* If @call is a kfunc or helper call, fills @cs and returns true,\n19672:\t * otherwise returns false.\n19673:\t */\n19674:\tbool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,\n19675:\t\t\t\t struct bpf_call_summary *cs)\n19676:\t{\n19677:\t\tstruct bpf_call_arg_meta meta;\n19678:\t\tconst struct bpf_func_proto *fn;\n19679:\t\tint i;\n19680:\t\n19681:\t\tif (bpf_helper_call(call)) {\n19682:\t\t\tif (bpf_get_helper_proto(env, call-\u003eimm, \u0026fn) \u003c 0)\n19683:\t\t\t\t/* error would be reported later */\n19684:\t\t\t\treturn false;\n19685:\t\t\tcs-\u003efastcall = fn-\u003eallow_fastcall \u0026\u0026\n19686:\t\t\t\t (bpf_verifier_inlines_helper_call(env, call-\u003eimm) ||\n19687:\t\t\t\t\tbpf_jit_inlines_helper_call(call-\u003eimm));\n19688:\t\t\tcs-\u003eis_void = fn-\u003eret_type == RET_VOID;\n19689:\t\t\tcs-\u003earg_slot_cnt = 0;\n19690:\t\t\tcs-\u003eimplicit_slot_cnt = 0;\n19691:\t\t\tfor (i = 0; i \u003c ARRAY_SIZE(fn-\u003earg_type); ++i) {\n19692:\t\t\t\tif (fn-\u003earg_type[i] == ARG_UNUSED)\n19693:\t\t\t\t\tbreak;\n19694:\t\t\t\tcs-\u003earg_slot_cnt++;\n19695:\t\t\t}\n19696:\t\t\treturn true;\n19697:\t\t}\n19698:\t\n19699:\t\tif (bpf_pseudo_kfunc_call(call)) {\n19700:\t\t\tint err;\n19701:\t\n19702:\t\t\terr = bpf_fetch_kfunc_arg_meta(env, call-\u003eimm, call-\u003eoff, \u0026meta);\n19703:\t\t\tif (err \u003c 0)\n19704:\t\t\t\t/* error would be reported later */\n19705:\t\t\t\treturn false;\n19706:\t\t\tcs-\u003earg_slot_cnt = btf_proto_slots(meta.btf, meta.func_proto);\n19707:\t\t\tcs-\u003eimplicit_slot_cnt = 0;\n19708:\t\t\tif (meta.kfunc_flags \u0026 KF_IMPLICIT_ARGS) {\n19709:\t\t\t\tconst struct btf_type *func = btf_type_by_id(meta.btf, meta.func_id);\n19710:\t\n19711:\t\t\t\t/* the prototype without implicit args, see is_kfunc_arg_implicit() */\n19712:\t\t\t\tcs-\u003eimplicit_slot_cnt = cs-\u003earg_slot_cnt -\n19713:\t\t\t\t\tbtf_proto_slots(meta.btf, btf_type_by_id(meta.btf, func-\u003etype));\n19714:\t\t\t}\n19715:\t\t\tcs-\u003efastcall = meta.kfunc_flags \u0026 KF_FASTCALL;\n19716:\t\t\tcs-\u003eis_void = btf_type_is_void(btf_type_by_id(meta.btf, meta.func_proto-\u003etype));\n19717:\t\t\treturn true;\n19718:\t\t}\n19719:\t\n19720:\t\treturn false;\n19721:\t}\n19722:\t\n19723:\t/* LLVM define a bpf_fastcall function attribute.\n19724:\t * This attribute means that function scratches only some of\n"
} |
| 41/3 | 2026/11/02 00:47 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 11007 output: 34 thoughts: 1150 Thoughts: **Analyzing the BPF Verifier Liveness Change** Okay, so I'm looking at this BPF verifier change and trying to understand its implications. The core seems to be in the `compute_insn_live_regs` function, specifically how the "use" mask for registers is calculated. Previously, it looked like: `use = GENMASK(min_t(u8, cs.arg_slot_cnt, MAX_BPF_FUNC_REG_ARGS), 1);`. Now, there's a subtraction: `cs.arg_slot_cnt - cs.implicit_slot_cnt`. And I see `cs->implicit_slot_cnt` is being populated within `bpf_get_call_summary`. The reasoning is that for kfuncs with implicit arguments (marked with `KF_IMPLICIT_ARGS`), the BPF program *doesn't* actually pass those arguments. The verifier itself injects them. So, the original liveness analysis was incorrectly marking those implicit argument registers as "used" *before* the call instruction because the code was treating them as though the BPF program was setting them. This is confirmed by those test comments in the commit. Now, a critical question I have: Does this change introduce any potential for security issues? Specifically, can it lead to uninitialized memory access? Since `cs` is a stack variable, that seems unlikely, but I'll double-check this point, especially looking for any data leaks to userspace. First, I need to confirm `cs` isn't sent to userspace. Good, `struct bpf_call_summary` is in `include/linux/bpf_verifier.h` - an internal header. And looking at `bpf_get_call_summary` itself, `cs->implicit_slot_cnt` is initialized explicitly, so no issues there. Okay, let me check other callers of `bpf_get_call_summary` because I need to verify that all of the fields of the `struct bpf_call_summary` are properly initialized. Scanning the code, I see: 1. `record_call_access` just reads `arg_slot_cnt`, no problem there. 2. `compute_insn_live_regs` - This is the primary function this changes! 3. `call_params_mask` - Looks like it also uses `arg_slot_cnt`. 4. `mark_fastcall_pattern_for_call` - uses `cs.fastcall`. I'll re-examine how `bpf_get_call_summary` is set: In the cases where it returns true: all fields in `struct bpf_call_summary` are initialized *before* returning. If it returns false, the caller doesn't use it, which is safe. So, the change *seems* safe. The core concern was the potential for uninitialized memory being used in the liveness calculation, but this doesn't seem to be an issue here. The code paths all appear to initialize `struct bpf_call_summary` correctly. I'll need to go back and check how the liveness calculation works in general though, to be sure I'm not missing anything. Specifically, I'll review `liveness.c` more thoroughly, just to get a good mental model. |
| 42/3 | 2026/11/02 00:47 | tool | grepper |
0mArgs:{
"Expression": "compute_insn_live_regs",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/liveness.c=2476=static int callee_subprog(struct bpf_verifier_env *env, const struct bpf_insn *insn)\n--\nkernel/bpf/liveness.c-2481-/* Compute info-\u003e{use,def} fields for the instruction */\nkernel/bpf/liveness.c:2482:static void compute_insn_live_regs(struct bpf_verifier_env *env,\nkernel/bpf/liveness.c-2483-\t\t\t\t struct bpf_insn *insn,\n--\nkernel/bpf/liveness.c=2662=int bpf_compute_live_registers(struct bpf_verifier_env *env)\n--\nkernel/bpf/liveness.c-2701-\t\tfor (i = start; i \u003c end; ++i)\nkernel/bpf/liveness.c:2702:\t\t\tcompute_insn_live_regs(env, \u0026insns[i], \u0026state[i], ret_reg_pair);\nkernel/bpf/liveness.c-2703-\t}\n"
} |
| 43/3 | 2026/11/02 00:47 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 13197 output: 34 thoughts: 18 Thoughts: Okay, let's dive into this. Here's my summary, presented as a stream of consciousness, as you requested: **Investigating `bpf_compute_live_registers` Usage** Alright, time to get my hands dirty. I need to understand the practical applications of `bpf_compute_live_registers`. It's a key function in BPF, and I want to see exactly how it's being leveraged in the codebase. Let's trace its calls. I'll need to use my usual tools - likely a combination of static analysis, code searching, and perhaps even some dynamic debugging if necessary, depending on the complexity. The goal is to identify all the contexts where this function is employed. I'll look for patterns, common usage paradigms, and any potential optimizations that could be made based on how it's currently being integrated. I'm especially interested in whether its usage aligns with best practices and if it's being applied effectively across the different BPF subsystems. No stone unturned. Time to dig in and uncover its secrets. |
| 44/3 | 2026/11/02 00:47 | tool | grepper |
0mArgs:{
"Expression": "bpf_compute_live_registers",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/liveness.c=2482=static void compute_insn_live_regs(struct bpf_verifier_env *env,\n--\nkernel/bpf/liveness.c-2626-\t\t\t} else if (bpf_pseudo_call(insn)) {\nkernel/bpf/liveness.c:2627:\t\t\t\t/* a static callee's reads are added in bpf_compute_live_registers() */\nkernel/bpf/liveness.c-2628-\t\t\t\tsubprog = callee_subprog(env, insn);\n--\nkernel/bpf/liveness.c-2661- */\nkernel/bpf/liveness.c:2662:int bpf_compute_live_registers(struct bpf_verifier_env *env)\nkernel/bpf/liveness.c-2663-{\n--\nkernel/bpf/verifier.c=23875=int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,\n--\nkernel/bpf/verifier.c-24086-\nkernel/bpf/verifier.c:24087:\tret = bpf_compute_live_registers(env);\nkernel/bpf/verifier.c-24088-\tif (ret \u003c 0)\n"
} |
| 45/3 | 2026/11/02 00:47 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 13815 output: 38 thoughts: 48 Thoughts: Here's my analysis of what I'm thinking: **Examining BPF Register Liveness** Okay, let's dive into the guts of this BPF register liveness computation. I need to understand the function `bpf_compute_live_registers` and how it's being utilized within the kernel. The goal is to get a handle on the register state at various points within BPF programs. Since I'm very familiar with the kernel code layout, I'm heading straight for lines 2660-2720 of `kernel/bpf/liveness.c`. This should give me a good, focused view of the core logic. I'm expecting to find the algorithm, possibly some supporting data structures, and the context in which this function operates. I need to understand its inputs, outputs, and any potential side effects. Knowing how to efficiently track register liveness is absolutely key for optimal BPF program execution, so this is a worthy pursuit. I anticipate finding some bit manipulations, control flow analysis, and potentially some inter-procedural analysis to determine register usage across branches and function calls within a BPF program. |
| 46/3 | 2026/11/02 00:47 | tool | read-file |
0mArgs:{
"File": "kernel/bpf/liveness.c",
"FirstLine": 2660,
"LineCount": 50
}Results: {
"Contents": "2660:\t * Store result in env-\u003einsn_aux_data[i].live_regs.\n2661:\t */\n2662:\tint bpf_compute_live_registers(struct bpf_verifier_env *env)\n2663:\t{\n2664:\t\tstruct bpf_insn_aux_data *insn_aux = env-\u003einsn_aux_data;\n2665:\t\tstruct bpf_insn *insns = env-\u003eprog-\u003einsnsi;\n2666:\t\tstruct insn_live_regs *state;\n2667:\t\tint insn_cnt = env-\u003eprog-\u003elen;\n2668:\t\tint err = 0, i, subprog, start, end;\n2669:\t\tbool changed, ret_reg_pair;\n2670:\t\n2671:\t\t/* Use the following algorithm:\n2672:\t\t * - define the following:\n2673:\t\t * - I.use : a set of all registers read by instruction I;\n2674:\t\t * - I.def : a set of all registers written by instruction I;\n2675:\t\t * - I.in : a set of all registers that may be alive before I execution;\n2676:\t\t * - I.out : a set of all registers that may be alive after I execution;\n2677:\t\t * - insn_successors(I): a set of instructions S that might immediately\n2678:\t\t * follow I for some program execution;\n2679:\t\t * - associate separate empty sets 'I.in' and 'I.out' with each instruction;\n2680:\t\t * - visit each instruction in a postorder and update\n2681:\t\t * state[i].in, state[i].out as follows:\n2682:\t\t *\n2683:\t\t * state[i].out = U [state[s].in for S in insn_successors(i)]\n2684:\t\t * state[i].in = (state[i].out / state[i].def) U state[i].use\n2685:\t\t *\n2686:\t\t * (where U stands for set union, / stands for set difference)\n2687:\t\t * - repeat the computation while {in,out} fields changes for\n2688:\t\t * any instruction.\n2689:\t\t */\n2690:\t\tstate = kvzalloc_objs(*state, insn_cnt, GFP_KERNEL_ACCOUNT);\n2691:\t\tif (!state) {\n2692:\t\t\terr = -ENOMEM;\n2693:\t\t\tgoto out;\n2694:\t\t}\n2695:\t\n2696:\t\tfor (subprog = 0; subprog \u003c env-\u003esubprog_cnt; subprog++) {\n2697:\t\t\tstart = env-\u003esubprog_info[subprog].start;\n2698:\t\t\tend = env-\u003esubprog_info[subprog + 1].start;\n2699:\t\t\tret_reg_pair = bpf_ret_reg_pair(env, subprog);\n2700:\t\n2701:\t\t\tfor (i = start; i \u003c end; ++i)\n2702:\t\t\t\tcompute_insn_live_regs(env, \u0026insns[i], \u0026state[i], ret_reg_pair);\n2703:\t\t}\n2704:\t\n2705:\t\t/* Forward pass: resolve stack access through FP-derived pointers */\n2706:\t\terr = bpf_compute_subprog_arg_access(env);\n2707:\t\tif (err)\n2708:\t\t\tgoto out;\n2709:\t\n"
} |
| 47/3 | 2026/11/02 00:47 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 15079 output: 29 thoughts: 24 Thoughts: Here's my take on those thoughts, tailored for an expert audience: **Digging into Live Register Analysis** Okay, so I need to understand the lifecycle of those live registers. I'm going to track down the usages of `env->insn_aux_data[i].live_regs`. My initial thought is to identify all the places in the code where this specific structure member is read or modified. This should reveal the core logic impacting the register liveness analysis, I need to understand its role in determining register allocation, instruction scheduling or optimization passes further on down the line. I'm expecting this will take me to the points in the compiler or runtime where register allocation, spill code insertion, or perhaps even dataflow analysis occurs. By tracing the uses, I should be able to reconstruct the data flow and reason about the validity of these calculations. |
| 48/3 | 2026/11/02 00:47 | tool | grepper |
0mArgs:{
"Expression": "live_regs",
"PathPrefixes": [
"kernel/bpf/"
]
}Results: {
"Output": "kernel/bpf/liveness.c=2398=int bpf_compute_subprog_arg_access(struct bpf_verifier_env *env)\n--\nkernel/bpf/liveness.c-2458-/* Each field is a register bitmask */\nkernel/bpf/liveness.c:2459:struct insn_live_regs {\nkernel/bpf/liveness.c-2460-\tu32 use;\t/* registers read by instruction */\n--\nkernel/bpf/liveness.c=2476=static int callee_subprog(struct bpf_verifier_env *env, const struct bpf_insn *insn)\n--\nkernel/bpf/liveness.c-2481-/* Compute info-\u003e{use,def} fields for the instruction */\nkernel/bpf/liveness.c:2482:static void compute_insn_live_regs(struct bpf_verifier_env *env,\nkernel/bpf/liveness.c-2483-\t\t\t\t struct bpf_insn *insn,\nkernel/bpf/liveness.c:2484:\t\t\t\t struct insn_live_regs *info,\nkernel/bpf/liveness.c-2485-\t\t\t\t bool ret_reg_pair)\n--\nkernel/bpf/liveness.c-2659- *\nkernel/bpf/liveness.c:2660: * Store result in env-\u003einsn_aux_data[i].live_regs.\nkernel/bpf/liveness.c-2661- */\nkernel/bpf/liveness.c=2662=int bpf_compute_live_registers(struct bpf_verifier_env *env)\n--\nkernel/bpf/liveness.c-2665-\tstruct bpf_insn *insns = env-\u003eprog-\u003einsnsi;\nkernel/bpf/liveness.c:2666:\tstruct insn_live_regs *state;\nkernel/bpf/liveness.c-2667-\tint insn_cnt = env-\u003eprog-\u003elen;\n--\nkernel/bpf/liveness.c-2701-\t\tfor (i = start; i \u003c end; ++i)\nkernel/bpf/liveness.c:2702:\t\t\tcompute_insn_live_regs(env, \u0026insns[i], \u0026state[i], ret_reg_pair);\nkernel/bpf/liveness.c-2703-\t}\n--\nkernel/bpf/liveness.c-2714-\t\t\tint insn_idx = env-\u003ecfg.insn_postorder[i];\nkernel/bpf/liveness.c:2715:\t\t\tstruct insn_live_regs *live = \u0026state[insn_idx];\nkernel/bpf/liveness.c-2716-\t\t\tstruct bpf_iarray *succ;\n--\nkernel/bpf/liveness.c-2746-\nkernel/bpf/liveness.c:2747:\t\tinsn_aux[i].live_regs_before = mask_lo(in) | mask_hi(in);\nkernel/bpf/liveness.c-2748-\t\t/*\n--\nkernel/bpf/scev.c=447=static bool reg_alive_at(struct bpf_verifier_env *env, u32 reg, u32 insn_idx)\n--\nkernel/bpf/scev.c-449-\tstruct bpf_insn_aux_data *aux = env-\u003einsn_aux_data;\nkernel/bpf/scev.c:450:\tu16 live_regs = aux[insn_idx].live_regs_before;\nkernel/bpf/scev.c-451-\nkernel/bpf/scev.c-452-\treturn reg \u003c MAX_BPF_REG\nkernel/bpf/scev.c:453:\t ? (BIT(reg) \u0026 live_regs)\nkernel/bpf/scev.c-454-\t : test_bit(reg - MAX_BPF_REG, aux[insn_idx].live_stack_before);\n--\nkernel/bpf/scev.c=1865=static bool scev_reg_alive(struct bpf_verifier_env *env, struct bpf_verifier_state *st, u32 r)\n--\nkernel/bpf/scev.c-1867-\tint insn_idx = bpf_frame_insn_idx(st, st-\u003ecurframe);\nkernel/bpf/scev.c:1868:\tu16 live_regs = env-\u003einsn_aux_data[insn_idx].live_regs_before;\nkernel/bpf/scev.c-1869-\tint spi;\n--\nkernel/bpf/scev.c-1871-\tif (r \u003c MAX_BPF_REG) {\nkernel/bpf/scev.c:1872:\t\treturn BIT(r) \u0026 live_regs;\nkernel/bpf/scev.c-1873-\t} else {\n--\nkernel/bpf/states.c=420=static void __clean_func_state(struct bpf_verifier_env *env,\nkernel/bpf/states.c-421-\t\t\t struct bpf_func_state *st,\nkernel/bpf/states.c:422:\t\t\t u16 live_regs, int frame)\nkernel/bpf/states.c-423-{\n--\nkernel/bpf/states.c-427-\t\t/* liveness must not touch this register anymore */\nkernel/bpf/states.c:428:\t\tif (!(live_regs \u0026 BIT(i)))\nkernel/bpf/states.c-429-\t\t\t/* since the register is unused, clear its state\n--\nkernel/bpf/states.c=493=static int clean_verifier_state(struct bpf_verifier_env *env,\n--\nkernel/bpf/states.c-502-\t\tu32 ip = bpf_frame_insn_idx(st, i);\nkernel/bpf/states.c:503:\t\tu16 live_regs = env-\u003einsn_aux_data[ip].live_regs_before;\nkernel/bpf/states.c-504-\nkernel/bpf/states.c:505:\t\t__clean_func_state(env, st-\u003eframe[i], live_regs, i);\nkernel/bpf/states.c-506-\t}\n--\nkernel/bpf/states.c=986=static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_state *old,\n--\nkernel/bpf/states.c-988-{\nkernel/bpf/states.c:989:\tu16 live_regs = env-\u003einsn_aux_data[insn_idx].live_regs_before;\nkernel/bpf/states.c-990-\tu16 i;\n--\nkernel/bpf/states.c-1001-\tfor (i = 0; i \u003c MAX_BPF_REG; i++)\nkernel/bpf/states.c:1002:\t\tif (((1 \u003c\u003c i) \u0026 live_regs) \u0026\u0026\nkernel/bpf/states.c-1003-\t\t !regsafe(env, \u0026old-\u003eregs[i], \u0026cur-\u003eregs[i],\n--\nkernel/bpf/verifier.c=18780=static void collect_linked_regs(struct bpf_verifier_env *env,\n--\nkernel/bpf/verifier.c-18787-\tstruct bpf_reg_state *reg;\nkernel/bpf/verifier.c:18788:\tu16 live_regs;\nkernel/bpf/verifier.c-18789-\tint i, j;\n--\nkernel/bpf/verifier.c-18792-\tfor (i = vstate-\u003ecurframe; i \u003e= 0; i--) {\nkernel/bpf/verifier.c:18793:\t\tlive_regs = aux[bpf_frame_insn_idx(vstate, i)].live_regs_before;\nkernel/bpf/verifier.c-18794-\t\tfunc = vstate-\u003eframe[i];\nkernel/bpf/verifier.c-18795-\t\tfor (j = 0; j \u003c BPF_REG_FP; j++) {\nkernel/bpf/verifier.c:18796:\t\t\tif (!(live_regs \u0026 BIT(j)))\nkernel/bpf/verifier.c-18797-\t\t\t\tcontinue;\n--\nkernel/bpf/verifier.c=23837=static void log_program(struct bpf_verifier_env *env)\n--\nkernel/bpf/verifier.c-23844-\nkernel/bpf/verifier.c:23845:\tverbose(env, \"Program dump (scc? loop_header? idom insn#: live_regs_before):\\n\");\nkernel/bpf/verifier.c-23846-\tfor (i = 0; i \u003c insn_cnt; ++i) {\n--\nkernel/bpf/verifier.c-23858-\t\tfor (j = BPF_REG_0; j \u003c BPF_REG_10; ++j)\nkernel/bpf/verifier.c:23859:\t\t\tif (insn_aux[i].live_regs_before \u0026 BIT(j))\nkernel/bpf/verifier.c-23860-\t\t\t\tverbose(env, \"%d\", j);\n"
} |
| 49/3 | 2026/11/02 00:47 | llm | kmsan-evaluator |
0mModel:gemini-3.8-flash Args: null Results: null Tokens: input: 17695 output: 301 thoughts: 1829 Thoughts: **Analysis of the BPF Verifier Patch and KMSAN Impact**
Okay, let's break this down. My goal is to determine if this BPF verifier patch introduces any uninitialized memory risks that KMSAN needs to flag.
First, let's remember what this patch does. It adjusts how the verifier handles "implicit arguments" in kfuncs. Specifically, it tweaks the `bpf_compute_live_registers` function to correctly track which registers are live *before* a BPF instruction, particularly in the context of kfunc calls. Before the change, the verifier incorrectly marked registers corresponding to implicit arguments as used by the call, which messed with the liveness analysis used for scalar evolution (SCEV) and state pruning. The patch fixes this by subtracting `implicit_slot_cnt` from `arg_slot_cnt` when calculating the "used" registers for the call in `compute_insn_live_regs`.
Now, the crucial question: does this introduce a KMSAN vulnerability? KMSAN detects uninitialized memory reads, so we need to check if this patch makes uninitialized memory accessible. Here's my checklist:
1. **Kernel structures to userspace:** Nope. The `struct bpf_call_summary` is a purely internal verifier structure. It lives on the stack within the verifier and is never copied to user space. Every field, including the new `implicit_slot_cnt`, is explicitly initialized within `bpf_get_call_summary`. So, no risk of leaking uninitialized data to user space.
2. **Conditional logic based on uninitialized data:** No dice. The `cs.implicit_slot_cnt` field is initialized to 0 in all paths through `bpf_get_call_summary`.
3. **Complex data structures with uninitialized fields:** Nope. The patch is about a local stack variable (`struct bpf_call_summary`) and how we calculate a bitmask. No complex data structures are allocated, and no fields are left uninitialized.
4. **Bounds checks exposing uninitialized memory:** Not at all. The patch modifies a bitmask used by liveness analysis. It does not introduce any changes to buffer handling, sizes, or memory accesses. The potential for an arithmetic underflow issue in the calculation, even if present, would manifest as a logic error in the verifier's register tracking, which is already thoroughly checked by existing verifier logic and standard bug detectors.
Let's double-check all aspects:
* Is any memory copied to userspace? No.
* Is any variable left uninitialized?
The `struct bpf_call_summary cs;` is on the stack within `compute_insn_live_regs`. When `bpf_get_call_summary(env, insn, &cs)` is called, the struct's contents are fully initialized whether it is a helper call or a kfunc call.
* Are there any info-leaks to userspace? No.
* Does BPF program execution use uninitialized kernel memory due to this patch? No. The liveness analysis is for verifier optimization/post-processing; not BPF program execution. All BPF program register initialization happens in the `do_check` abstract interpretation step, and the verifier *already* ensures that registers are initialized before they're used. This liveness analysis only influences optimization, not safety.
Therefore, given this analysis, I am very confident this patch does *not* introduce any new uninitialized memory risks that would trigger KMSAN. KASAN and existing verifier checks are more than adequate to catch any potential issues. KMSAN is not necessary here. I will proceed to call `set-results` and provide this justification.
|
| 50/3 | 2026/11/02 00:48 | tool | set-results |
0mArgs:{
"KMSANReasoning": "The patch updates BPF verifier liveness analysis (`compute_insn_live_regs`) to account for implicit kfunc arguments. Specifically, it adds an `implicit_slot_cnt` field to `struct bpf_call_summary` so that registers corresponding to kfunc arguments injected implicitly by the verifier are not marked as read/used by the caller program in the live registers bitmask.\n\nKMSAN is not needed because:\n1. `struct bpf_call_summary` is a verifier-internal structure allocated on the stack; its fields (including the new `implicit_slot_cnt`) are explicitly initialized to zero in all branches of `bpf_get_call_summary()` before being read.\n2. The structure is purely internal to the verifier and is never copied to user space (no infoleak risk).\n3. The change affects only the calculation of register bitmasks used for liveness/SCEV analysis during BPF verification. It does not introduce, touch, or expose any uninitialized heap, stack, or page memory, nor does it alter buffer sizing or bounds checking in kernel memory copies.\n4. Any potential issues with verification logic or register state tracking would be caught by verifier assertions and standard tests/KASAN. KMSAN provides no unique detection value here.",
"NeedsKMSAN": false
}Results: {
"KMSANReasoning": "The patch updates BPF verifier liveness analysis (`compute_insn_live_regs`) to account for implicit kfunc arguments. Specifically, it adds an `implicit_slot_cnt` field to `struct bpf_call_summary` so that registers corresponding to kfunc arguments injected implicitly by the verifier are not marked as read/used by the caller program in the live registers bitmask.\n\nKMSAN is not needed because:\n1. `struct bpf_call_summary` is a verifier-internal structure allocated on the stack; its fields (including the new `implicit_slot_cnt`) are explicitly initialized to zero in all branches of `bpf_get_call_summary()` before being read.\n2. The structure is purely internal to the verifier and is never copied to user space (no infoleak risk).\n3. The change affects only the calculation of register bitmasks used for liveness/SCEV analysis during BPF verification. It does not introduce, touch, or expose any uninitialized heap, stack, or page memory, nor does it alter buffer sizing or bounds checking in kernel memory copies.\n4. Any potential issues with verification logic or register state tracking would be caught by verifier assertions and standard tests/KASAN. KMSAN provides no unique detection value here.",
"NeedsKMSAN": false
} |
| Total Calls | Total Tokens | Avg Tokens | Total Duration (Seconds) | Avg Duration (Seconds) |
|---|
| Total Calls | Total Duration (Seconds) | Avg Duration (Seconds) |
|---|